Here’s three suggestions for sure-fire performance:
Nuts — easy to eat, easy to transport, good source of all kinds of good stuff.
Protein Bars — you shouldn’t overdo these, but they’re a handy way of refuelling on protein if you need to occasionally bridge the gap between meals.
Dried fruit — go with figs or prunes. Gets points because they won’t go mushy in your bag, your body will respond to the sugar hit, and it adds a bit of fibre to your diet.