Many Swiss Army knives have a can opener. You hook a part of it under the can rim and it acts as a lever for the small knife blade above it. You simply work your way around the can, cutting the lid a bit at a time. I've done it many, many times. It's safe and easy.

https://www.google.com/search?q=swiss%20army%20knife%20can%20opener&ie=utf-8&oe=utf-8&client=firefox-b-m