3HP left - what to squeeze in?

Hi all, to cut a long story short(er), I bought a complete rack on Reverb for a very good price and have it in my posession. Its basically a Stepper Acid sequencer with Behringer System 100 minus the Sys 100 Sequencer and Portamento modules. I love it already and have only just scratched the surface. Takes me back to the Maplin 5600 I built in 1981 but no longer have (sigh!)
It has a 3HP gap top right and I have been wondering what to squeeze in. It sounds great with the Stepper Acid running just 1 voice so have another voice to play with. I asked the seller (a Eurorack enthusiast) what it needed next and he said more modulation.
I was debating whether to add some effects or another sequencer, hence why I put the Erica Pico Seq in but it could easily be the DSP or what...?
I have a keystep so could use that instead of another Eurorack sequencer and have a Digitakt so dont need percussion in the rack just yet.
I like musical sequences, arpeggios, syncopated rhythms.
I will be adding another Rackbrute case in due course but not ready yet! Suggestions very much appreciated for the 3HP top right gap anyway.

Perhaps a different Pico module: the Pico Input. Very useful to get line-level sources into the system.

I never thought of that. You mean as other sounds to manipulate? I have a Korg Minilogue XD which has CV and sync inputs so could presumably hook that up?

Certainly, but also anything with only audio out (guitars, many keyboards, etc). I have always found it odd that the XD (keyboard version) doesn't have CV/Gate out, only in.