Maybe you can buy some fresh stuff like bananas and avocados, which are a little heavy and thus can ease the hunger.
Do you ear nuts and raisins, they have plenty of sugar so you get enough calories. In Switzerland you can buy a mixture called 'Studentenfutter' (studend's food) because it is also supposed to be nourishing for the brain, maybe they have it in Prague too.
I eat nuts etc and will probably bring a stash of nut bars with me! Ad astra per aspera
