If/when it becomes a problem (or perhaps even before then), it would be pretty easy to pass laws restricting commercial drone use within city limits.

Personally, I very much doubt that drone deliveries will be anything other than a gimmick or a convenience that is cost prohibitive for almost everyone.

• It's almost always going to be more mechanically efficient to roll something than fly something
• Liability for damages resulting from flying mishaps seems likely to outweigh damages resulting from traditional driving deliveries
• Drones can only function in ideal weather conditions (too windy/wet/cold = damage to drone, delivered item, or both)

Little delivery robots that drive on sidewalks seem much more likely than flying drones—and even then, I just don't see the need. We already have cost-effective shipping networks (Postal Service, UPS/FedEx, Amazon) that visit routes multiple times a day, and humans on standby ready to deliver food or groceries to your doortstep for subsistence wages—it's going to be hard to find and justify use-cases for single-delivery drones/robots of any kind.