I have a couple of friends who play guitar and ukelele. I'm envious of the compact size, light weight and portability of their instruments. Sometimes we go on road trips/ camping, and I would love to be able to contribute something musically, perhaps drum tracks, some pad sounds, a bass line, or occasional leads

So what's the most "portable" accompaniment instrument?
-MIDI accordion (love the idea, but not sure I could learn Stradella bass)
-Omnichord or it's successor the Q-Chord
-Korg MicroArranger driven by battery supply?
-Keytar or lightweight controller MIDI'd to my BK-7m (again, both driven by battery)
-A battery-powered Yamaha? (you have to go back to the '90s to find one that allows user styles and on-bass chords)
Yamaha QY-100 portable sequencer?
Roland PMA-5?? What are some other portable "beat boxes" like this?

What auto-accompaniment instruments have you used that are highly portable and usable without house current, at least for a couple of hours? An unusual question, thanks in advance for sharing your thoughts!!