It's important to always pay sustenance workers in cash. Anything else is inconsiderate and rude. People in those jobs are usually dearly hanging on to the margins and causing all of their income to be taxable for no good reason is heartless.

It's also just generally a good idea to carry cash. Electronic payments have too many failure modes, not the least of which are power and connectivity. (Currently posting this from a disaster zone which is thankfully still connected to the internet.)