+1 for i/o modules - a lot of WTF? sounds come from bits and bobs that I process. I’ve got a rode m3 that I can plug straight into my i/o module, sample whatever on the rack, and then mess around with it.
For ambiental noise, I’ve found that a lot of cross modulation of oscillators can really bring static sounds alive. I have a doepfer 143-4 that i patch into itself for complex ambiences and drones.
Modules that can feedback are also a massive bonus. I use a string reverb for this, but also analog delays can create amazing feedback loops that you can then filter, modulate, delay again, and generally have fun with.