A local food distributor delivers all of their products by bike. They use a recumbent cargo bike with a large (two cubic meters) trailer that has an electric assist. If you quibble, it's not a bicycle, it's a tricycle. Also, it's not all human powered, but it is a lot better than using a cargo van, especially here in the Northwest with our hydroelectric-based grid. Also, my carpenter neighbor generally parks his van at the worksite and rides his bike back and forth whenever possible.

I don't know if either of these options would work for you, but there may be solutions out there if you want to use a motor vehicle less. To pick up on DC's point, there is an electric-assist system for the Xtra-cycle that may work for you. I'm actually not a big fan of electric assist, but sometimes a bit more power greatly enhances the utility of a bike.