That's why I suggested wristbands: easy to verify. (Paid) staff handing out food can check them easily as they are on the wrist holding a plate, anyway.
Given that we can not adapt on the fly, I would not overcomplicate things. Either you pay for the whole time or you eat elsewhere. Same as Vaumarcus.
Splitting into three time frames is already nice IMO.
As I said in the past, leftovers should go to charity if at all possible.
Sent by mobile; excuse my brevity.