In the beginning, postal carriers were photographed with satchels, but I've always liked the look of the sorters inside some mail wagons I've seen, including my inspiration. There wasn't a lot of room, but I was able to add a few cubbyholes. These wouldn't necessarily be reserved as one per household on the route but a way to sort along the way.
I added a window lock from my stash of interesting hardware (not sure where I even got them or the manufacturer). The lock bar actually slides, though it doesn't matter much for my non-working window. I'm thinking the hook on the top would hold the window open, maybe? I'll definitely add small hinges to complete the look of my non-operating front window.