Any idea how to practice at work ?

Any ideas how I can learn a song without actually having my guitar on me ? I have some spare time at my job sometimes I have an hour or two that I I’m just sitting doing nothing. I can’t pull out a whole guitar and start practicing but if I can find a mini neck with strings that I can pluck and press on ,,it don’t have to sound loud at all I and I practice playing . At least be able to memorize what frets to play on certain songs which seems to be the most time consuming part . Any suggestions. I just wanna spend the time learning so when I get home I can hope on my guitar and be ready to go . Or maybe an app or something .