This kid had all the right points.
emphasis on using headphones, not eating eachothers food, and the do not enter sign.
however what I quoted is the biggest load of horse shit. Share everything you feel comfortable sharing. my room mate and I get along very well and we share pretty much everything.. drinks, silverwear/plates/cups, xboxes/games/controllers. I would start getting pissed off if I needed something like a cup or water bottle and my room mate got all territorial on me.
when it comes down to it, you are living together and theres plenty of time for you to get them back with whatever it is you borrow/take.