Something easy to cook and light.
I take rat pack meals as I'm nut fussy about what I eat. Food is fuel. You can get similar meals from camping shops. They are not cheap £4-5 each. The supermarkets do some in the bag ready meals which are good, think they are called "look what i found".
Snacks are good to, nothing worse then being hungry when out. I take flapjack, dried fruits and nuts.