On a ride with that many people, you're going to need variety.
For the fast guys, it's grab and go if they even stop. If you're going to step it up for that crowd, I'd say musette bag handups and pre-filled water bottles. I'd make that a pre-paid option, with a different color wrist-band and routing from the other folks for the handups. That'd be awesome.
We had a spring ride in Indiana that featured hot potato soup every year, and we all looked forward to that on a crisp spring day. Made in large pots, served in cups, it was delicious and could be downed quickly if so desired. Unless it's hot, I think that's a great compromise. Potatoes digest well, but it's hot and can be enjoyed.
For the other end of the spectrum, we're talking good food enjoyed while sitting down. Preferably with a live local band. These folks aren't going to bolt out of the sag stop and toss their cookies in 30 minutes; they're going to chat, eat, chat, roll out easy, and ramp up their speed over the next hour. You don't want to waste their time waiting in line, but they don't need to be in a rush while eating. Forget about appropriateness for the activity. You could go with chili, spaghetti and meat sauce, gourmet burgers, burritos, arroz con pollo. A Paris-Brest pastry for everyone would have some panache.