We all know you can open most cheap padlocks with a shim
made from an aluminum can. Well, perhaps we didn't all know, but such is the case. However, when I'm standing outside my gym locker after working out and realize I've bonehead forgotten my combination or key, chances are I don't have a premade shim or a pair of scissors, razor blade, marker or a template on me. However, I can probably find a can around the place. Here is a way to make an inferior but working shim using only a can and your hands.
DISCLAIMER: Obviously only do this with your own locks or for others you know have rightful access to what you are opening yet somehow managed to get locked out.
Step 1: Flatten out the can
Flatten the can somewhat, either the whole thing or one side. Just squeeze it until it's fairly flat, try not to crumble it too much, we're hoping to get a fairly flat piece of metal out of the deal.
Step 2: Make a point and rip
Fold the flat part sharply into a point. Perhaps wiggle it back and forth a few times until the metal starts to give a little, showing through the label. Then flatten it and rip it as one would a piece of paper.
Step 3: Keep ripping
Keep ripping through the can until it's mostly severed. It will rip easily once the initial tear has been made. If you can, attempt to get one (or more) sides fairly straight as this will be useful later. Be careful, this stuff is pretty sharp, so try not to brush against the edges or corners.
Step 4: Remove top/bottom
Rip off the top and bottom, leaving you with a nice sheet of aluminum. Toss top/bottom if you'd like.
Step 5: Reduce to small piece
Keep doing the same thing you did at first, fold a small point, possibly wiggle it a bit and tear as straight as possible. Reduce it to a piece about half an inch by three inches. It's not terribly picky, but one side needs to be as straight as possible. If it goes bad, pick another sliver from the larger piece and try again.