I don't know if a carry-out tray will encourage a sale,(after all, no one asks for a tray before they order) BUT the customers definately appreciate it when the concession attendant asks "Would you like a tray for that?" The customer definately appreciates it. We have those plastic trays like fast food restraunts use. We have probably 30 of them, and put a sticker "Please return to the vending stand" on them, so we can hopefully get them back right away for other patrons to use. I would recommend a bright color, red, orange just in case a customer leaves one in the theatre, then they get picked up right away before someone trips over it or something.