Sounds like you're planning to use a tray, but in case you're unable to get one or ever forget to take it with you, here's a tip I read on another thread. Fill a plate with food, then take an empty plate and put it upside down on top of your plate like a lid. Then you can place another plate with food on top of that, and stack multiple plates to carry in this way. Haven't tried it myself, but seems like a good solution in a pinch.