Many pocket Swiss knives and multi tools have a tin opener, however, few people seem to know how to use it.
It is actually rather simple. Take the knife into your right hand – this is important, since the opener blade is sharpened to one side. Put it on the lid and start pushing the blade into the lid, using the can side as support. It is not exactly fast and convenient, but still better than nothing.
Continue to work the lid until you reach the end. The edges may be sharp, so be careful while taking out the contents.