I can't help with the quantities, but I can tell you that two things that are labor intensive, but have gone over EXTREMELY well in one ride I participated in plus one I helped putting on (just not on the food side) - were peeled hard-boiled eggs (rest stop food hardly ever has sufficient protein), and cold washcloths, if the weather's going to be hot. Wet the towels, chill or even freeze them the night before, and then take them to the rest stop in a cooler. (The ride I participated in had them rolled up and handed out in zip-loc bags, but besides being wasteful, I can't see how that's really necessary.) Have another bin for the used towels, then you can wash them after the ride and use them year after year.

I and my riding buddies raved over these two items at the ride I participated in, so much so that I brought them over to the ride I helped with, and we got rave reviews from our participants, too.