Can opener
You can usually dig up a can opener in a rental kitchen. But what if you can't find one? Those cans are tough! Opening one without a can opener is nearly impossible (and maybe dangerous, depending on how you go at it).
This can opener weighs almost nothing, and will get you out of the "can't find a can opener" jam.
See the little folding blade on the can opener? The pointy tip is what is going to cut open the metal lid of the can. Grab your can and hold it firmly on the counter. Now, there is a notch on the can opener at the base of the folding blade. That goes under the rim of the can. Get it under the rim, with the point of folding blade on the lid of the can, right near the rim. Now twist the opener, so that the point pierces the metal lid. Twist it all the way down, so that you have made your first cut. Now twist the opener so that the blade comes back up, nearly out of the can. Move the notch on the opener so the blade is at the edge of the cut you just made and twist it down again to make your next cut. Proceed in this way around the rim.
It takes a bit of time, but it sure is better than trying to open the can with a screwdriver and hammer you found in the garage.