Attending Summer Institute for TFA means I'll be returning to a living arrangement I haven't had to deal with since freshman year, the dreaded tiny shared dorm room with communal bath down the hall. Most high school seniors who're headed off to college in the fall can look forward to a similar housing situation. In the coming months they'll be inundated with advertisements for all manner of products that are touted as "must haves" for college students. Don't rush out to buy everything on these lists; some items are really necessary for everyone, some are useful but optional, and some are pointless. You probably have much of what you need at home and needn't rush out to get new things. Here are a few items I've found to be particularly important for comfort and productivity while living in dormitories.
Good bedding: You may not be getting tons of sleep, but you'll want to be able to get a good night's rest when you have the chance. Dorm beds are often spectacularly uncomfortable. A good pillow helps, as does a mattress pad, whether a cheap egg crate, a fiberbed, or fancy memory foam. (Twin and twin xl memory foam pads can often be purchased very cheaply a few months after school starts when stores put all of their leftover back-to-school merchandise on clearance so it might be worthwhile to start shopping while you're in high school.) Don't buy sheets before you're sure whether you'll have an extra long mattress; I've always had standard twin beds and been able to use bedding from home.
Shower shoes: Pick up some $1 flip-flops to avoid the ickiness of bare skin against the floor of a shower dozens of other people also use. If your dorm floor has a tub and you are likely to take baths, buy some generic bathroom cleaner and a sponge to wash it before and after each use.
Ear plugs: It's pretty much a given that you and your randomly matched roommate(s) will have diametrically opposed musical tastes and sleep schedules. Even if you somehow manage to luck out in that regard, the night you need to get a major paper written will coincide with the tunnisboule world championships*, which will conveniently take place directly outside your door. If you plan to do any studying in your room, ear plugs are your friend. It may take some experimenting to find a brand of ear plugs that are comfy and fit well enough to block noise effectively.
Headphones: Ear plugs are good, but they don't block all sound. Your roommate will be far less likely to bludgeon you to death if you don't constantly subject her to your musical preferences, especially when you need to listen to something to keep you awake at 3 a.m. while you finish up a paper and she needs some rest before a 7:30 a.m. honors chem test.
A computer: You may be required to purchase a computer with certain specs as a condition of enrolling. Even if a computer isn't mandatory, seriously consider getting one; it'll make your life much easier. The computer labs at my university are often full, some have limited hours, and most require trudging across campus, not something you'll be eager to do in the middle of the night. It's much nicer to know you have a dedicated place to work that will always be available.
Laptops can be convenient, but I opted for a desktop, used it as my sole computer for over 3 1/2 years, and am still very happy with my decision. If you need a computer primarily for research, writing papers, and email, you can probably find a package deal with monitor and maybe a printer that'll do everything you need for less than $500 if you wait for good sales. More RAM is generally a good thing, a nice monitor is a plus for watching dvds, and a cheap tv tuner card is nice if your dorm has free cable and you like that sort of thing. You might consider OpenOffice as an alternative to the expensive Microsoft Office if you aren't hopelessly attached to Excel for sciencey uses.
If you shop around and consider what you actually need, starting college needn't be hugely expensive. Plan on buying the minimum and purchasing additional items over the first few weeks as you get a better sense of what you'll use.
*Tunnisboule was invented in fall 2004 by some people who lived down the hall from me. It is a team sport played with brooms with dustpans duct taped to their handles, some sort of ball, and the elevators at either end of the hallway as goals. The rules are fairly flexible, and you're allowed to hit people with your broom handle if you feel like it. There's a lot of yelling involved.