I would take a can of coconut cream, the type with no added water, and also wrap up tightly in foil about 8 Tbsp of protein powder and stick it inside a couple of ziploc bags one inside the other for extra protection, with all air squeezed out. That should be tumble/water proof. When it's time to eat just open the can of coconut cream and stir the protein powder in. That'd be about 1000 calories based on the coconut cream I buy (Ayam). You'd probably need more meals but at least there's an idea, although it depends what your macro requirements are - if you're on the higher carb end of the spectrum that might not fit your goals.
Primal since May 2012. Loving life and down 50lbs.