Fact: College is expensive. Further fact: You have some control over how expensive. Most of what I'm about to tell you is based on common sense, but sometimes it helps to see common sense written out. And yes, I have done all of these things, and many of them I do/consider on a regular basis.
1. Minimize how much you pay the college itself: the lump sum of tuition, housing, and board. The first step here is securing scholarships. (Actually, the first first step is to go to a college that isn't ridiculously expensive, but good luck with that. If you're going to a four-year, residential college, the theoretical [pre-financial-aid-package] price tag will be at least $30,000 a year.) Do well in school. Pay attention to schools that give you good financial aid packages, whether need-based or merit-based. Apply for outside scholarships--not the "[Brand Name Here] $20,000 College Sweepstakes! Just fill out your name and GPA and click here!!" things, but little local ones that fewer people will apply for. These you actually have a meaningful chance of winning.
Living in a multiple-occupancy room means each person spends less money for housing. Divided doubles are very nice.
As for food, Oberlin has a number of meal plans depending on whether or not you're in OSCA, whether you live on or off campus, and whether you're enrolled full-time or not. Most meal plans come with a number of meals per week and then "flex points" that can be spent at DeCafé, the grocery/deli in the student union building. You can also use flex points to buy more meals, but it's expensive. If you have fewer meals in your plan, you have more flex points, and the plan overall costs less. Therefore, if you're on the edge between two meal plans (say, the twelve-a-week and fourteen-a-week plans) and you think that you would usually eat twelve meals in dining halls and the rest in your room or at a friend's co-op, but sometimes you might not have the time--I'd say go for the twelve meal plan and fill in the occasional gap with flex points rather than routinely waste a meal. It's cheaper overall and you have more flex points, which translates to more customized sandwiches or smoothies or snacks to keep in your room. Keep in mind, though, that where you eat and when can be a big part of social life. Don't be a hermit: eat with people.
At Oberlin, of course, you can also skip out on paying the school for room and/or board altogether if you get into a co-op. Co-ops cost less and come with a pre-made social circle.
2. Minimize travel costs. I kinda failed this one, personally, because I live in Washington (state, not D.C.) and I'm going to school in Ohio. Oops. The trade-off there is that I don't go home that often; staying on campus over Spring Break saves at least $400 round-trip.
3. Minimize what you spend on textbooks. Buy used--and I don't mean from the Oberlin bookstore, though that's a decent resource; most books can be found cheaper online. My favorite source, though, is the Oberlin Classifieds, a sort of Craigslist just for Obies. The intro neuro textbook sells new for eighty to a hundred dollars, plus shipping; I got it for thirty. I've also used the Classifieds to sell my textbooks on to other Obies after I've used them. It's sort of a local-economy thing, and also much, much less expensive than buying from the bookstore.
If you use the Internet and buy early, the bargains won't be snapped up yet and you can save a lot. Buying later, especially if you're looking for a textbook many colleges use, means prices will be higher, and that you'll have to pay for rush shipping to get your books before class starts. That means this strategy only works when you know what classes you'll be taking. If you intend to utilize add/drop, don't do this--use the Classifieds instead. Maybe someone who bought early had to drop the class you just added and is trying to sell off their books!
4. Minimize stuff. The less you have to haul, the better (and the less you have to ship, the cheaper)! Don't bring tons of books--that was my rookie mistake. Bring a board game or two and you'll make friends, but a pack of cards does just as well.
Don't buy all-new supplies for college. It's fun, and the ads make everything look so pretty, but really, you just need things that are comfortable and useful. You probably will have to buy sheets for an extra-long twin bed, but you can use comforters and blankets that you already have. Most school supplies you can swipe from home: paper, notebooks, erasers, pens. If there's a small wastebasket that never gets used, swipe it. Pillows? I don't know about you, but we have tons of extra pillows. Swipe 'em. Same for towels and washcloths. (I did a lot of swiping.) About the only thing you will probably have no choice but to buy is some kind of shower tote.
On a related note: do not buy dorm furniture. There is no room. Maybe a small auxiliary bookcase or something--maybe--but dorm rooms come with a bed, desk, chair, and a few bookshelves either on the wall or attached to the desk, and that uses up the space very nicely. Perhaps if you have a quad (and thus a common room) you can coordinate something with your roommates, but otherwise, you'll have an expensive new nest chair and nowhere to put it. (The lovely, roomy, coordinated dorm rooms you see in ads do not exist anywhere in the real world, or at least not in any college-owned housing.)
5. Don't spend money. You're in college! Everything is free (or nearly so), and everything is right there. This is particularly true at Oberlin, where you can go to concerts, comedy shows, plays, musicals, lectures, art shows, performance art pieces, junior and senior recitals, Quiddich games, Circus, contra, swing dance lessons, yoga, meditation, "Coffee with Krislov," poetry readings, open mic nights, and more just by looking at fliers or the online events schedule. Then, of course, there are the unscheduled events--spontaneous sing-a-longs or Frisbee games or Giant Robot Movie Night in Sci-Fi Lounge. And, of course, the best entertainment is talking late into the night with your friends.
This is not to say that you should never, ever, ever go out to eat or to the movies (the Apollo comes under the category of "nearly free" anyway), but do it with friends and remember it's a treat, not a routine thing. I know I've gone out to eat more in just the past year than my parents ever did in college (averaging about twice a month if you count mochas at Slow Train), and I'm not quite sure how I feel about that.
I know people who do so less frequently, I'm sure (especially those in co-ops), but I think many people--most?--go out more than I do. I'm not sure why, except that the Starving Student Ethic seems conspicuously absent from Oberlin. I think to some degree the college culture has changed, perhaps in response to college-cost inflation: we're all in debt to the tune of tens of thousands anyway, so why not go out for dinner? Some of it might be the result of a more entitled culture--Obies are overwhelmingly the children of fairly wealthy, college-educated people, which I think was not the case at my parents' college. If you're coming from a background of going through the Starbucks drive-through every morning, you've got a different set of expectations (anthropologically speaking, it's called a habitus) about how much it's appropriate to spend when and where on what. Just remember that if you buy a $2.50 coffee every weekday--pretty cheap for coffee--that's $50 a month or a semester's textbook outlay every semester.
On the other hand, going out doesn't mean you have to spend a lot. Lots of the restaurants have great lunch prices. And sometimes you aren't the one paying: the Computer Science department paid for two lunches for my winter term modeling class, for instance, and Professor Darling very kindly took all us research assistants out to lunch. Emma took her Competitive Computer Programming ExCo out for pizza on the department's dime, too. (What is it with the CS department and free food?) Add in generous visiting relatives and splitting dessert with friends and twice a month doesn't look as hopelessly self-indulgent as it did at first.
So, a slight correction to the rule above: Don't spend money unreasonably. Don't stop yourself from having fun--a $3 admission fee or the cost of Feve tots should not bar you from an enjoyable evening. Just make sure it all is enjoyable, and don't get in the habit of throwing money around.
6. Don't buy stuff. It's not only experiences that are free or dirt cheap, especially at Oberlin. You probably don't need all that much. Obviously, you need boring necessities--soap for you, dishes, and laundry; Tylenol; tissues. Those you can get at Gibsons' or Ben Franklin's. Ben Franklin is usually less expensive.
MindFair Books is a used bookstore attached to Ben Franklin--a dangerously accessible trove of books--but if you really want to save money, use the library. Oberlin has four libraries (the main one, Mudd; the science library; the Conservatory library; and the art library). Whatever Oberlin doesn't have, it can order via OhioLink (to other Ohio colleges) or Illiad (a nation-wide inter-library loan program). This isn't just for academic works--I've mostly used it to get comics. The Oberlin Public Library is a fun place, too.
Most other things you can probably borrow from someone for a while--people tend to be very generous--or find in the Free Store, a cave of wonders in the basement of Asia House. This is exactly what it sounds like: a room full of (clean) clothes, books, widgets, and other items that other students don't want anymore and have donated. It's run by students. You can take whatever you like for free! (They do appreciate donations of quarters to wash the clothes, though.) I have an unfortunate habit of forgetting to go there when it's open and remembering about it when it's not.
The Oberlin Classifieds are probably going to be your friend here too. I've seen everything from furniture and cars to clothes to a metronome advertised there.
Also, along the lines of the eating-out concept: make sure you would really enjoy what you're buying. Know if you need to own it or if listening to it online or borrowing it from a friend would do just as well. If you'll use it repeatedly for a long time, then get it; otherwise, don't. Common sense, but I want to cover all the bases here.
7. Enjoy yourself. Spending all your time stressing about how you'll pay for your college experience leaves you no time to enjoy the college experience. Be practical about how much you spend, but don't lose focus on the important thing here. Think about what you're saving your money for (besides next semester's bill). Presumably, you want more time at college--specifically, more time at Oberlin. What's the draw? Learning things? Spending time at a busy, crazy place with interesting, talented people? Becoming the world's foremost stage lighting technician? Whatever it is, you've already given yourself permission to spend a whole lot of money and four years of your life pursuing it. You can take advantage of that input. Relax and enjoy it.