At my current job I have a fairly cheap (but surprisingly nice once set up) Fender Squier Jazz bass next to my desk. Bass is my first real instrument, so it doesn’t require much thought for me to pick up and jam on, plus when it’s not plugged in to an amp it’s fairly quiet so I don’t feel like I’m bothering my coworkers. I have a little usb interface on my desk that typically just gets used as a headphone amp, but I can also plug into that if I want to hear it in my headphones (I have Guitar Rig on there) or record something I come up with.