You want to take everything you need, but you have to make some tradeoffs between what you want to take and the space you have. If something can have multiple uses, for instance, that becomes a valuable thing. People don't ordinarily think of these decisions as math, but those kinds of decisions are very mathematical. Packing is also related to the concept of optimization. Math has a lot to do with efficiency, trying to find the most efficient way to do things.
Optimization is related to finding the most efficient method of solving a problem.
Like setting up the tent. Setting up the tent involves both spatial relationships and problem solving. Putting up a tent is like doing a puzzle. You've got these pieces, you've got the shape. It's a great problem solving activity.