I can make a few suggestions, based on experience.
1. Advanced notice. It sounds like you did that, but did you........?
2. Talk to the right person. You can call the coach, the school, the local cat groomer, but eventually, you need to talk to the person who actually runs the concession stand. Most of the time, your first call can give you the right person. It's a heck of a lot better than the coach forgetting about it, and then at the last minute running up to the already packed concession stand and telling the first volunteer worker who otherwise does nothing more than volunteer work in the concession stand.
3. Be specific. If you want 20 meals, say 20, if you want between 20-25, well that is where it gets a little hinky. Make 20 and be short? Make 25 and don't know what to do with the others?
4. Be specific. If you don't want the kids to have sodas, say so. If you don't care, say so. I tend to not offer soda for the athlete unless the coach specifically says that it is ok. It's gatorade or water.
5. Let em know whether you want to pick em up individually, or to pack everything in a big box to go. I've had kids show up to get theirs, passed out 4 or 5 and then the coaches show up to take the box to go. Can get confusing that way, when some already have theirs, some don't.
6. In this case, let the school know that there were problems. That is unacceptable service. Granted, you won't get 4 star quality service, but there should at least be a minimum expectation. Including that the bags contain food. I'm sure the booster club, Junior class, teachers drinking fund, etc. would like to know that they messed up so that maybe they can fix it in the future.
7. If you are coming to Gordon, call me, I'm your guy, I'll hook you up.