I have a https://www.modulargrid.net/e/ladik-e-510-envelope-follower which gives Trigger, Gate and Envelope. I recently used some filtered noise (a crackle type sound) to trigger and run an entire patch. If you happen to have any Piezo contact Mics they can also be used with an envelope follower, at its most simple just tapping on a Mic via the Ladik E-510 can be used to affect the modulation of something else via its envelope. All good fun.
Grab a Mutable Instruments Ears for a bit of Mic-Pre-amp and envelope follower in one.
Enjoy your spare HP, don't rush to fill every last space, this is not like filling sticker books. Resist the urge to 'complete' your rack, its never complete so just relax.