Here got the tiers https://www.grab.com/sg/driver/deliver/
Looks like walking and PMA are the ones most limited. Also think these guys more likely to get tips from the customers if the customer is nice. But their area of operation will be severely limited.
Actually coffee shops can become like primary school dispense coke/sprite/fanta/etc to save costs but they won't cos they will use this opportunity to eat more $$$...