The thinner pieces of metal from inside the anti-theft white plastic things on DVDs, expensive tools, etc work way better (and less likely to cut you) than aluminum can bits.
With quite a few locks, you could do the same with an ordinary credit card (or other plastic card of the same dimensions) if the bolt is exposed to the outside (which is common on older doors with worn/deteriorated trim, since the piece of trim blocking direct access to the bolt is usually a separate piece of wood from the rest of the door frame, allowing one to slip the card between it and the frame).