Shawn, As far as concessions.. I would suggest a few things.
First, don't have a lot of different prices, ( ie if you have 5 kinds of candy bars, regardless of cost, if they are within a close range of one another, make them ALL the same price, and make a little more on some, and profit a little less on others)
Secondly, Have ONE SIZE of drinks and popcorn. We always make iced tea and lemonade, and sell bottled water. There's a lot of profit in " make as you go" powdered drink mixes, as opposed to cans of beverages. It also solves the problem of not having cases of leftover stuff, or what to do with already wet, chilled cans, and so on. Also, if you do a lot of canned beverages, people always want what you don't have. Keep it simple, they will buy what you have.
Next, and probably most importantly.... sell TICKETS for food and beverages at a SEPARATE table. The people handling food don't want to handle money, and it makes the lines go MUCH faster. We use different colors for different items and/or price points.
ANother point.. Tape off a " middle row" in the grass.. so people can navigate back to the concessions without stepping on/over/around other guests. Also, " tape off" a seating area for handicapped guests. Anyone with a wheelchair will appreciate it, and will especially appreciate that " aisle" I just mentioned!
If I think of anything else, I will let you know!
ps.. and if it starts to rain.. sell garbage bags as raincoats!

ha ha