Or guitar + foot bass + singing:

Or piano + foot drums + talkbox:

People often hear what I'm doing with Kingfisher and ask how it works, but when I show them they say they couldn't do it because they're not good enough at multitasking. But I didn't start off being able to do this either, and it's a skill you can learn.

If you're not convinced of that, consider organ. There are maybe a million people who have learned how to play separate keyboards with both hands, and a third keyboard with their feet, all while moving between settings ("stops"). And piano, where the left hand and right hand do very different things, probably has tens of millions of players. So if you're interested in learning how to do this, you probably can: this is within the general capabilities of humans.

This kind of multitasking is all something I taught myself, so there may be better paths, but here's what I do. The core of it is that I have much more physical ability to do things than conscious attention to coordinate them with. So I need to get aspects of my playing out of my conscious attention, to where I can control them as larger chunks that I can combine it with other uses of my conscious mind. When I have something I want to push down to my body like this I use three steps. I play it:

1. In isolation, until it's solid. I start with something very simple, because recovering from errors would require moving back to conscious attention.

2. While distracting myself with something non-musical. This forces my body to figure out how to continue the physical action with minimal demands on my conscious attention. And if I fail at that the music will audibly stumble.

3. In combination with other musical actions. There seem to be parts of my brain that are only for music, and in this step I'm forcing these actions to learn to share.

For example, when I was trying to learn how to play left-hand rocking octaves on piano at the same time as right-hand chords, I started by just doing the left hand. Initially I wasn't very good at it, and it took my full mental capacity to keep it going. As I got better, I started intentionally distracting myself. I'd typically read: the goal was to move the action down a level, the way walking is, so I could free up my conscious attention for something else. Then, once I could continue a solid left hand while reading, I'd start combining it with right hand playing. This was harder, since both draw on the musical parts of my brain, but still less work than if I'd skipped the distraction stage.

It's critical to break each of these steps across multiple sessions. Learning doesn't just happen while practicing: there's a consolidation that happens between sessions, where something that was just out of reach at the end of the last session often comes easily the next time. If you try and push rapidly through the stages before there's been time for that consolidation, you'll probably get frustrated.

A related kind of multitasking I've worked on is talking while playing. It feels like I've just always been able to do this, but Julia reminded me I used to practice playing chords on mandolin while trying to have a conversation with her. I'd play a very simple pattern, one that was so simple it used as little conscious capacity as possible, and try to talk. Initially, as soon as the rhythm of the speech conflicted with the rhythm of the instrument I'd mess up one or both, but over time I got smoother at both. I'd always prioritize keeping the mandolin steady, since in all the circumstances where I planned to use this it was much more important for the music to be consistent. Over time I got to where I could fluently call chords, and even discuss more complex musical plans (usually with Amy).

Overall, I'm much worse at multitasking when playing melody. I used to think that this was because I've always been a much stronger rhythm player, but this is also a pattern I see in others: seeing fiddlers struggle to get a single word out while playing can be pretty funny. Testing just now with my fiddle and playing an easy tune, I can talk about anything but there are small gaps in my speech. On a tune that's closer to the edge of my ability I can feel that my concious mind is needed to keep it all going, and if I try to talk anyway the tune falls apart. When I'm calling while playing at parties I do a mix of simple tunes and falling back to rhythmic shuffles while getting words out. It helps that I'm doing easy dances and don't need many words. When I think about my model of multitasking it makes sense that melody would be harder: it's going to be easier to offload something to my fingers if it's simpler and repetitive, and that's usually not what you want in a melody! So I'd recommend starting with offloading accompaniment.

If all of this sounds too hard, the simplest accompaniment of all is stomping your foot in time with the music. It's moderately musical on its own, a gateway to various forms of percussive accompaniment, and helps you avoid mental patterns where you produce syncopated rhythms by stretching your sense of time instead of playing with where the notes land.