I get salads at Sweetgreen (one of the referenced cashless retailers) periodically. On two separate occasions I've been behind some stranger in line who didn't realize the place was card only, so I paid for their salad with my card and they gave me the cash. It is a weird policy, but I understand why they don't want to deal in cash.

Interestingly the flip side of this is cash only places. New York is also a huge user of Venmo for those times when you only have a card, but the place is cash only. Often if you don't want to have to leave to find an ATM and pay an ATM fee someone else will pay your bill in cash if you Venmo them the money. The problem of a cash free, or cash only place is easily solved in both cases with a little cooperation with your fellow New Yorkers.