Too late for all that.....I bring all my gear

So what's the most "portable" accompaniment instrument?
-MIDI accordion (love the idea, but not sure I could learn Stradella bass)
Indeed, a great idea. If you already play the keyboard, the bass will come real easy. When it comes to Stradella, you only need to learn one key!

-Omnichord or it's successor the Q-Chord
A couple of times, I thought about getting one, but even the most expensive model feels like a toy....

-Korg MicroArranger driven by battery supply?
I haven't used mine for a long time. I don't think it's battery opperated though you could find a battery pack for it.

-Keytar or lightweight controller MIDI'd to my BK-7m (again, both driven by battery)
I have a USB model by Alesis. You can use a USB-MIDI Din converter to directly connect to the BK-7m. My son said it looks so 80s...

-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?

Well, if you are a guitar player and need rhythm backing, the QY-100 would be nice, but I think you are looking for something that you can play yourself. I'd say vArranger with a small midi controller would work well. It has the feature of finger on bass you are talking about.

Roland PMA-5?? What are some other portable "beat boxes" like this? My, that's an old module/sequencer. I still have two units. Once again, aren't you looking for something that you can play live yourself?

Dexibell: I played different models at NAMM. They didn't have a WOW effect on me. As a piano player, I always lean towards 76 or 88 keys. I have my eyes on the Numa Compact 2. No hammer action, but only 15.6 pounds, lots of features, great sounds, and built-in speakers.