In a tin - SAK (one with a saw for my preference) or a small Spyderco - the Grasshopper slippie is a good one.

Bear in mind weight as well - I love the Boker Subcom, but it is very heavy for a small knife

As ever, these are all points on a spectrum - given the choice, a full sized axe, saw, knife and multitool etc would be with me in a crisis. However, as others have said, it's only useful if you have it when you need it