Singing Valentines for valentines day. You'll make a killing. make little cardboard hearts and make the students wear them when they delever a song, and have recordings of the students singing which song they choose available during lunches or in the mornings so students can hear what they're ordering.
also, there's cards and chocolate and roses and the like. special occasion stuff usually does pretty well. Our FFA sells four cookies for a dollar during lunches and makes tons. (they use an empty chemistry room to bake them in. so when i walk to chemistry I'm dying of hunger. :p)
Some theatres, and our choir, sell CDs of the musical performances they do and sell them at the production. It's kind of a risky thing, but if you have they fascillities (you don't nessicarrily need a recording studio) go for it.
We do an evening of scenes where our theatre productions students (or the advanced theatre students) choose a scene out of a play and hold their auditions together and direct. we usually put it all together in a week (not including the time it takes to select, read, and cut a script)
Also, it can depend on what production you're doing. Like selling chocolate and candy bars for willy wonka (which we're doing next year! ^_^), or cat in the hat hats for seussical, etc.
try and stay away from the normal stuf like figurines, pies, cookie dough and stuff because you'll almost always end up ordering more than you sell. (our theatre's fridge is full of pies... :/)
"We're afraid to talk to you now, because anything we say causes you to burst into song." - My friends