On the tools, just look at every nut and bolt that you might need to remove to do an emergency repair, or re-tighten if it comes loose, and make sure you got it with you.
As far as a cheap bag, I just use a waterproof backpack from Walmart, and set it on the floorboard with the top handle hooked on the bag hook. About as simple as you can get, but it works! The rear rack on a Super 8 is mostly for looks. It's a royal pain to tie anything to it without it shifting around on you.
