Prison phones are a hot emerging market that benefit from drone delivery.

They're not efficient ways to deliver to consumers, but to delivery units like the local post office they're remarkably efficient (especially for rural areas). The biggest cost savings to be had would be to deliver from a local warehouse to the nearby DU, where you would pay the last mile carrier to do the heavy lifting. The issue you run into is that there's no appetite for increasing the load at these units, so no appetite for innovation until the infrastructure improves.

I’ve always felt round things like sushi and burritos could be delivered by putting them into some kind of silicone fairing and firing them from a pneumatic cannon aimed by a computer, no need for autonomous flying robots.

That would definitely work for my burrito place, though I can see it from my front door, so a t-shirt cannon might suffice.

A civilized place would not permit the sort of noise pollution that a large-scale drone deployment would generate.