Noooooooooooooooooooo!!!!!!!!!!!!!!! I've got to have my M&Ms!!!
HA! Of course, of course.
You misread me. I didn't say "no sweets" at all! I have been on shoots where the crafty table was nothing but chips, cookies, and candy. No sustainable nutrition. That leads to a sugar and carb load that crashes in an hour and leaves crew members tired, cranky, and hungry. That's not to say that there shouldn't be chocolate (or red vines). I have a voracious sweet tooth, and I give into it far too often, but I also love to have munchies on hand that will stick with me.
Rik had mentioned nuts, as you did, but you also bring up a really good point with allergies. Nut allergies are more and more common these days, and the severety can be everything from "cannot ingest" to "cannot touch/be in the same room as" to "cannot touch someone else who has eaten them in the last 48 hours." Know your crew and plan accordingly.
If you have no nut allergies, a great midday snack (even if this sounds kindergarten-ish) is ants on a log: celery sticks with peanut butter, topped with raisins. Or even better, red ants on a log: same thing, but with craisins.
The hummus and salsa I mentioned are great to have as dips. Hummus provides protein, and good, fresh salsa is loaded with nutrients (the canned, processed stuff, not so much). Ranch and French onion dips are okay, but are empty calories.
And yes, the more water, the better.