You’ll want some Febreeze or an equilvilant product for when you need to destinkify some clothes and you’re out of quarters.
I second anyone who mentioned carpet or a rug. The tile floor in my dorm room would generate dust bunnies the size of actual bunnies 3.5 seconds after sweeping. The carpet keeps them subdued these days. Since it sounds like your room will be pretty small, call up carpet stores and ask about remnants they might have that match the size of your room.
Garbage bags will always come in handy for something, and if you use them in the way they’re intended, you won’t have to haul your whole icky trashcan out to the dumpster.
Bring a mattress pad. Do you have any idea what people have done on that mattress in previous semesters? I do. You’ll want to cover it with something before you put your sheets on it.
There will always be little things you need but forgot to bring. You will need scissors, glue, scotch tape, duct tape, a stapler, staples, paperclips, white out, a 3-hole punch, pens, #2 pencils, markers, crayons (maybe not need, but they’ll come in handy), and hiliters.
As for overnight visitors, the best thing you can do is talk about this with your roomie the very first day. Work out a policy that is agreeable to both of you. I would suggest giving your roomie adequate time to find somewhere else to stay if you want to have privacy with an overnight guest. Work out a signal that means “I would prefer that you not enter the room right now.” Don’t use it too often, or roomie will cease to respect it. These things are VERY important. I lost a roommate (formerly a reasonably good friend) because we did not set up visitor ground rules.
Have a flip-n-fuck available for non-intimate (;)) overnight visitors. Be sure roomie knows when they’ll be coming as well.
Good luck. Be sure to post any other questions you might have. Those of us living the dorm life are always thrilled to spread our superior knowledge.