I also happen to have a spare mini pc. It was originally a Chromebox that I converted to a TrueNas server a few years back, then abandoned it after building my current server.
I want to put it back in use but I'm not sure what to do with it and I'm hoping to get some suggestions.
It has 6gb of ram and 128gb of storage. I believe the current OS is TrueNas core but I can boot pretty much anything on it. I was thinking maybe a small SMB share for my family though we don't really need it.
You could install guacamole on your main server and configure WoL on the spare one, so you could access the spare one from remotely from outside the network. It might help you to not carry your laptop (if you use one) everywhere.
I recently had to travel and had to carry my work laptop and my personal laptop, and I ended up hurting my back. I am thinking of getting a spare mini PC which would be configured this way and would act as my main machine when I travel, so I don't have to carry my personal laptop everywhere. I would access it from my phone, or tablet, or from the work computer as I would have at least 2 of those devices on me anytime.