Depends how integral it is your business model and how difficult it is to police and clean up. I've seen
cabaret shows in black box theaters with carpet that are dinner-during-a-show events. Removable seats and dinner tables help keep the mess off the floor, and the mess that's on the floor is easier to clean up.
Fixed seats with carpeting is the worst. Very complicated to vacuum, and if someone makes a mess on the upholstery of a fixed seat, it can be a bear to try to clean up -- assuming it's even caught in time enough to do anything about it.
Fixed seats with concrete you can be a little more liberal with. Spills and gunk are easier to clean up on a concrete floor, and if you don't get to them right away aren't liable to stain.
I've seen a number of venues that do concessions where they sell them at 20min intermissions but only allow water back into the theater for the rest of the show. Seems to work well. If you do alcohol, it's even better if you take orders before the show so drinks can be prepared prior to the
intermission rush. I know one theater with a bar on every
level of the
house that has had decent success doing this (although to say there's oodles of money to be made on concessions is blatant lie, at least for
conventional theaters).
I know one theater who stores liquor on their premises but brings in an outside event company who brings in the bartenders, linens, and such. The event company holds the liquor license. They have a little
bit more success selling booze because it's in a higher class part of town, where they can hold annual fundraiser GALA's that are $600/plate. Their patrons will spend a good deal of money on drinks at
intermission (but only get to bring their drinks into the theaters in special circumstances, or in the studio theater removable seats and a hardwood floor.
On the other
hand -- if all you're selling is soda and cookies to a bunch of students and their parents, you'll have a hard time making a reasonable profit unless parents are donating their baked
goods for sale.
My general food/drink policy in theaters is pretty straightforward -- I don't care what you do so long as you aren't a distraction from the show, don't make a mess, and don't damage anything. If you do make a mess, that you make a diligent effort to clean it up. Hard to get an audience to stay tidy though, especially if you're presenting the kinds of shows where opening a cough
drop is considered a nuisance. Other types of performances lend themselves to more freedom of movement and behavior without disturbing the show or other patrons -- these are easier to allow food/beverage for without regretting it as much afterward.