Lufthansa used to have a little stand in the departure area where pax coud take whatever they wanted for the flight, from a selection of sandwiches, fruit, yoghurts, cooldrinks, and so on. They then popped into into a little carrier bag and took it on board.
This stunningly simple idea saved weight and cabin crew time, avoided waste, and allowed pax to get what they wanted. I often wonder why this did not become more widespread.