I bought one of Adafruit's Proto Cape Kit for my Beagle Bone Black so that I could put 3 relay circuits and pin headers on it. The double-sized PCB is supplied with separate pin headers that you have to solder on yourself.
It provides access to all of the pins but only SYS_5V is provided as a set of power lines and not VDD_5V, so limited current is available. However, this doesn't matter too much given that there is very little space for components.
I had to really squash everything in and use a lot of wires because there was no chance of creating an optimal layout: