For lure boxes, I am fond of velcro. Of course, Mike's bar works well too.
I always carry a 6-9 ft cam strap, mostly to due the same thing as the dog leash but it has came in handy several times when we get to the take-out and partners says "umm dude, I only have enough rope for one boat".
I bought a super magnetic tool holder, to hold pliers and such without being tangled in cords, but have yet to mount.
Outcast seat saddle bag-- the back pocket is nice to keep a sandwich up off the floor and dry, along with a rain jacket. The drink holders are handy too.