Some of this depends on your skills and repertoire, but....
There are a number of devices in the "porch board" realm that might be useful if you have a foot tap beat thing down. They are all basically a mic/transducer in a small box that you drum on with your foot. They are all devices meant to duplicate what some artists did anyway with their foot and sometime had mic'ed up in the old days. Some sound like a louder foot tap, some sound a bit more like a kick drum sound, and most need to be plugged into a PA/amp.
Ideal if you can do the taps and your stuff is more in the John Lee Hooker/Lightnin' Hopkins style of danceable solo guitar.
There were (and I think still are) a few folks who did the Jesse Fuller thing and actually used a kick drum they played along with guitar.
The kazoo/harmonica in the neck rack thing isn't quite rhythm support, but was another "give them something other than guitar all the time" solo guitarist solution from the old days.
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Creator of The Parlando Project
Guitars: 20th Century Seagull S6-12, S6 Folk, Seagull M6; '00 Guild JF30-12, '01 Martin 00-15, '16 Martin 000-17, '07 Parkwood PW510, Epiphone Biscuit resonator, Merlin Dulcimer, and various electric guitars, basses....
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