I'd probably assume that teachers may pay for their lunches weekly or monthly, instead of daily. These days a lot of things are put on someone's credit/debit card, and I'd wonder if teachers pay for their lunch that way. (Students living at college often pay for their meals by semester.) I may assume that part of teachers' benefits may be lunch. I may also wonder if the teacher realized s/he had no cash that day and made an arrangement with the lunch room cashier ahead of time.