For a tail bag, I found this "tactical" bag on eBay fairly cheap and modified the straps to allow a section of the removable shoulder strap to pass under the seat and be secured with a toggle made out of a section of aluminum tubing I had around. A wooden dowel could be used, too. The bag has cinch straps, two side pockets on either side of a larger main compartment and a smaller compartment on top - all zippered.
The bags come in black, sand, camo, etc... and would hold a small tablet.
My tank bag is a small magnetically attached one I found at Walmart of all places. =)
I don't have a photo, but it's small enough to work with the SCR's tank and big enough to hold a couple of bottles of water, a tire repair kit, etc..