This ruggedized, $120 Android phone has a big 10,000mAH battery and good-sized speaker for listening to music on lonely roads. It's got maps for multiple states downloaded and music downloaded so it doesn't need a data plan and is usually in airplane mode but with GPS on.
It's been pretty good, but the SOC is pretty slow. If I were to do it again, I'd splurge for a faster unit.
I'm still waiting for a computer with decent-sized flexible display that can be folded up and stuffed in a handlebar bag.