Picnics are usually relaxing affairs. This would be a bit more exciting, harkening back to caveman days when we had to chase our lunches, because you have to chase your lunch.
These lunchboxes have wheels and can move very fast. They move in unpredictable zig zag patterns, reverse, can even have
sensors that can tell when the person hunting them is close and take evasive action.
You'd actually have to work exhaustively hard to catch your lunch. All the lunches are lined up on the field, ready, set, GO!
Everybody at the picnic takes off trying to catch their lunchbox.
Just so you wouldn't have a sad turnout where a couple of people couldn't catch their lunch, they'd be programmed to slow down eventually, but the competition factor would still be there. Fastest to chase down lunch is the first to eat.
Like in olden times.
Could also do it with candy bars I guess. Kids might find that more fun.