I try to vary what I send.
We have wraps/pitas/rolls/turkish bread
otherwise he takes slices (savoury and sweet), bickies, fruit, popcorn in snap lock bags, muesli bars, pretzels, fruit bread, banana loaf, tin of baked beans, sometimes a bento box with a few bits and pieces vege sticks and dip, cheese pieces, etc (those insulated bags and an ice brick are great for keeping things cold), small packages of nuts.