What is the minimum plan for a one-day airport layover?

Asks what must be included in a layover route when weather and luggage can change the day.

For a one-day layover, I think the minimum plan is not a list of attractions. It is luggage storage, one compact neighborhood, an indoor fallback, meal area, return transport, and a hard airport return time. Without those fields, a rain shower or full locker can break the whole route. What do you include before you trust a layover plan?