The guitar, piano, and violin are some instruments that don't need accompaniment. I'm not sure if this would work for all musical instruments because it might get awkward. I feel like some instruments can only perform their best when mixed with other musical instruments.
It's possible, but I'm not sure each one of them will produce a pleasant sound. Try the triangle, for example. It seems weird to only play with that without any other instruments. I don't know.
It made me think, though.
The Kazoo is a serious instrument for solo improv.
I saw on YouTube how people tried playing the Kazoo. Some were decent, but others were something that I couldn't listen to until the end. It went well with Jazz, yeah, but it just doesn't work with mellow music.