A small tackle or Plano box for storing paints would work wonders.
Consider getting/making a wet palette too; preloading the wet palette with the colors you would need before your journey means you don't have to carry around all the paints you'd need, and they'll stay moist and workable throughout the day. The only downside to a wet-palette is that you have to store it flat, otherwise the water will leak out and/or the paints will just slide around the palette and make a mess. But if you have a backpack, just put it flat on the bottom or something and you should be good to go (just don't top the backpack!)
Brushes with caps can be stored in a pencil-case, and a mason-jar with a lid makes for a great water pot that you can seal up when you're done.
As for carrying your models, there's a variety of ways to do this. Realistically, just a small carry case or box with foam inside would do the trick, although bigger models might require alternative methods.
Chessex makes a great range of small miniature boxes that are very portable and can be tucked into a backpack without taking up too much space either.