In college I took to keeping toilet paper, toiletries, shampoo, etc. in my room to use when I needed it. My bathroom was the guest bathroom and my one roommate kept housing her sisters (3), plus all our friends that would hang out, some of their friends from home might stay a weekend. They would eat my food, use up my toilet paper, use my shampoo and toothpaste. Normally I wouldn't mind, but 50 cents here, 75 cents there, it starts to add up, and I couldn't get anyone to reimburse me. If they provided me with some TP when they went shopping or a gallon of milk or coffee, that would be fine, but that never happened, so I just stopped sharing. It didn't go over well.
Add the problem of retrieving money for long distance calls, as the bill was in my name, and so many people would use our phone. I would highlight the numbers I knew per roommate, then go after the friends to see who claimed the number. I'm the one that ended up eating the cost of $5 here, $10 there.
Needless to say, our rel@tionship fizzled at this point. It's good to try to maintain some even-ness where the money is concerned.