I bought a leakdown tester just so I had a hose to put air pressure into cylinders to replace valve stem seals, haven't used it for that yet but I have a lot of junk so I'll need it at some point, plus might do a leakdown on some things just to check health...
When we were camping the other day one buddy had a great use for snap ring pliers, pulling stuck sockets out of places, just stick it across the square drive and squeeze and pull... that'd come in handy for spark plug sockets here and there...
I have all sorts of tools I'll probably never use, I get bright ideas and order tools in anticipation then don't get to the projects... hopefully I'll catch up sometime soon though and can get to some of my projects...