If it’s not generative stuff, I record mouth sounds and then play the mouth sounds with instruments. Just make it up as you go along. Like for bass I record myself saying “Buhbib bibbadee bipda booba bipbip” and for pads it’s like “wwwoooOOOAAAAAAAAAAAAANNNNNnnnngg” and whatever. I never make them for specific songs, it’s just tons of short to shortish mouth sounds, and I might use them later on. My hope is that I remain irrelevant, and one day my descendants will find out that at least one of their ancestors was a complete moron, and this will be a humbling experience.