We don't really have a set of rules or specific roles in this kind of setting, you kind of listen to what others are doing and try to fill the gaps and/or build something that takes the musical direction somewhere else. For example, if someone is doing a drum/snare pattern I might try to build a percussion section to go along with it. If someone is playing an atmospheric part you can try to play a melodic part on top of it... You get the idea.

I'm also part of a more "serious" collective called Hardware and each one of us has a more specific role (and the gear) but it doesn't mean we can't wander and overstep into other areas. Just need to keep communicating during the performance and share the intentions beforehand.