When I was in the Marines and was single with much more free time and access to a large garage with all the free tools that I could need, I worked on my own Jeeps as well as Jeeps and Trucks of friends - mostly swapping out suspensions, adding "armor" (skid plates, brush guards, heavy duty bumpers...) but also installed lockers and switched out gearing. I didn't get to go off road as often as I liked but it was relaxing just to work on the stuff. These days I have the money to get some very nice equipment but don't have the time to work on things myself (or the free space).
Working with my hands now is limited to changing diapers or yard work and landscaping. I could spend a week trimming trees, pruning shrubs, planting flowers, etc. and never get tired of it.