I make 90% or more of my trips to the post office by bike. The smaller boxes are easy enough to fit in the saddle bag or panniers. The big ones, think surf boards and bikes, end up on the xtracycle for drop-off to UPS and FedEx. The medium ones are the challenge.
Today I had a vintage rack in a light but bulky box and improvised with some cord. It worked fantastic and had me thinking of some rack ideas John Cutter had designed a couple of years back. How are you getting the medium sized loads around by bike?
I use a CETMA 5-rail front-mounted cargo/porteur rack for small to medium boxes — anything that will fit between the levers of my drop handlebars. It’s been on my Surly LHT so it’s worked best for lighter (but bulky) loads that don’t fit in the rear panniers or would be awkward loaded on top of the rear rack. I’m currently building up a second-hand Kogswell w/ low-trail geometry, and will swap the CETMA to that bike in the hopes that it will be better suited to heavier loads.