A preconfigured raspberry pi, maybe with case, that automatically saves multitrack audio from a USB card. When you plug it into a Soundcraft Signature MTK audio interface (USB soundcard), at boot it waits for sound and reads all the live input channels and saves them to disk.

That way, we could record the full multitrack of our sessions very easily, and not necessarily need to have a laptop computer involved.

Edit: I would also pay for this if it shipped: http://www.samplerbox.org/ which is a sample-box for a MIDI keyboard. So also taking instruments off a laptop and into a smaller device.

I don't know why people don't sell prepackaged RPis for a mark-up for installing software that just boots and has sensible defaults.