So much has been written about using air and land-based autonomous vehicles to solve the "last mile" issues for Amazon, etc... It is already a crowded and well-funded space. My personal interest is in the more difficult large payload (over 400 pound) long-distance delivery market. Step one involves gas-powered fixed wing solutions, like what is being done in China.
The second step involves the creation of hybrid electric/gas powered drones, using the electric engines for vertical lift, and then a gas-powered prop for high-speed horizontal flight. One company pursuing that approach is Elroy Air. Here is a video of a small-scale proof of concept they developed. It is a creative approach, but because of the use of fixed wings for horizontal flight, involved a larger footprint for takeoff and landing.
The next step (and the most disruptive move) involves large-scale all-electric VTOL drones, able to handle delivery to remote and more urban locations. The big challenges here are low-weight engine/fuel solutions that handle large payloads cost-effectively. Boeing has tested its first platform targeting this market.
The big catalyst to enable all-electric solutions will be next-gen battery/supercapacitor technology. Unfortunately, that means a 5-10 year event horizon, but the market opportunity here is huge! This whole space will continue to remain on my active radar screen.