Read your specific dorm's housing page first. What appliances are prohibited varies dramatically — some schools ban microwaves in rooms but provide one per floor, some ban anything with an open heating element, some ban extension cords but allow surge protectors. What's already in your room also varies: most dorms include a desk, desk chair, and dresser; some include a mirror, a closet rod, or a shared microwave down the hall. Knowing this prevents buying things you don't need and shipping things that are banned.
Text your roommate at least two weeks before move-in. Not just about the fridge — about the things that actually cause friction when they're left unspoken: sleep schedules, overnight guests, shared food, preferred room temperature, noise while studying. These feel awkward to bring up over text before you've met. They feel significantly more awkward at midnight in week three when one of you is exhausted and the other has four people in the room.
Confirm your specific mattress size before buying any bedding. Twin XL is the standard at most U.S. schools — but not all. One email to your RA or one search of your housing FAQ prevents a bedding return trip before you've finished unpacking.