In China, they use E-bikes, I'm not sure why that wouldn't work here? Autonomous E-bikes shouldn't be that hard to manage, ya, they would need to balance themselves like segways, but I'm sure the tech is already there for it. There is no need for them to be full sized cars, even for crash safety...since it is just food that would get damaged in an accident.
Ebikes and small scooters make up the vast majority of deliveries in major cities. Can't remember the last time a delivery driver came in a car in NYC.
Some anecdata; E-bikes are definitely used in other major cities. I lived up against the Hudson in Jersey City and worked out of Manhattan and that was the primary means by which Doordash/Ubereats was moved around.
