My kid will eat a plain Wheatabix (the cereal) and treat it like it's -- edible, which go figure (my opinon: not so much, without some milk and maybe berries), and those are cheap (if doled out as snacks), and easy (if a store near you carries them).
Corn chips (the real kind, not fritos), string cheese. There ARE lots and lots and lots of edible packable fruits/veg so I go to those a bunch -- small carrots, raw snap peas, cherry tomatoes, grapes, apples, bananas, berries -- really, why limit yourself to 2 servings? Active kids are hungry kids. Nuts if they are old enough and there aren't allergy concerns. Chickpeas in a small tupperware container (or roasted). Peanut butter sandwich crackers (make your own).
Edited to muse on the OP's comment
This is the problem, they already have 2 pieces of fruit a day as part of crunch and sip. They eat this around 10 and then have recess a little later so need something different. It seems like a lot of food but they eat it all.
(emphasis added)
So -- um, why do they need something different? That's a serious question, and it's motivated by the one thing I've learned as a parent, which is, don't go making problems out of things that are not problems (enough problems will occur without needing your help). Clearly, we as parents worry about our kids' diets, and we should -- are you worried they aren't eating enough variety to achieve nutritional balance? Are their preferences narrow and you want to encourage them to broaden them? Both can be important goals (though arguably better tackled at times other than recess, but we work with what's available after all). But if your thinking is just, "I would be bored by this much _________ ." or "I would want more variety in my diet" -- well, I'm sure you would. But lots of kids aren't/don't. I mean for 1.5 schools years I sent my son to school with exactly the same sandwich (peanut butter on whole wheat) day after day after day and -- he ate it. And never said a thing. Then this year he asked for something different and we've switched to what he asked for which is -- drumroll, please: turkey and mayo on whole wheat.
We as adults get bored and value variety in a way that I think (many) kids do not. So if you're worried about this from your kids but they're eating what you're sending -- I'd just drop the worry and keep doing what you're doing because it's working.
