Ideas for meals for a 9 day camping trip with 50 people?

Sounds like your feeding an army, so look into what the army does. See if you can get hold of some ration packs. They can be quite boring but it's a good place to start. Everything else will depend on what facilities you have for cooking food and for storing it

Kabobs are good for at least a few meals. You can just cut up a bunch of meat and vegetables, have everyone assemble their own skewers, then pour some kind of bottled sauce on them and throw them on some foil on the grill. You can vary it by using different meats, different veggies and different sauces. Then just steam some rice in a pot of boiling water and you've got an easy meal with little clean up.

breakfast; scrambled eggs and toast pancakes cold cereal and fruit eggs and bacon beans and toast oatmeal waffles lunch; sandwiches wraps soup stew sloppy joes fish sticks, corn and mashed potatoes suppers; fish and fries hamburgers chicken and veggies roast beef and veggies spaghetti chicken pot pie

Burgers, Hot dogs...lol. If you bring a pot you can boil up some pasta, or potatoes. Of course you could fish and eat those.

Bring guns and eat whatever you shoot. Make it a wilderness survival theme and everyone will have a blast.