I'm going to use my roomie's aluminum foil
Are you allowed to? How do you feel about doing that?
There's a part of me that says I'm going to get in trouble for it , but there's another part telling me that he won't know.
I bet if you asked your roommate he'd be fine with it, seeing as roommates should share simple items like that.  Howeer, if you just take it without asking first that's stealing, which is wrong.  Just ask him!
I disagree on what you are saying.
That's okay, I just wanted to let you know that it'd be kinder and more considerate to ask to use his things. He may be saving that for something. How about trying to ask once, and see how you feel about it?