Hi Bob!
I bought a Willie & Max bag and attach it to the passenger backrest/sissy bar with a bungee. Works great, has a plastic liner and cost about $35. Not leather but looks like it. It's the one with two straps and a concho.
I've had the following in it: two bottles of water; or a rolled up T-shirt, baseball cap, cell phone, etc. (I do recommend that if you have a cold bottle/container that will dew-up on the outside, you put that in a big baggie to protect the bag.)
I can put it on the outside (back end) of the bar or on the passenger seat. Works well either way.
Bryna