When they were still young, my kids introduced me to the term "mad skills". If you had mad skills, it usually referred to some goofy ability, like hanging a spoon from the tip of your nose. But as they got older, we also used it to refer to something people didn't know about you. I have a couple of things that qualify as mad skills - besides silly tricks with spoons (I never could reliably do the nose trick, so settled for the spoon-glasses trick).
For one, I do my own photography, and I'm pretty decent at photographing wine bottles; this is very useful when you co-own a winery, since it saves money on hiring a product shot photographer. It has also been a real boon* when needing album covers for my CDs, and I'm responsible for shooting the photo of Shay and me used on the cover of Singer's Request, the one of Libby and me in my neighbor's Alpha Romeo for Carmony, and the photo of the Scottish Borders that I "posterized" for the Fortunate Strangers EP cover.
Another skill I occasionally indulge is stenciling. I cut my own stencils and then create freehand wall decorations, like the grapevines requested by my daughter for her sewing room. I love processes. The results are certainly gratifying, but really it's the "doing" that I love.
*A note about the word boon: I love this word, and we mostly use it to describe a beneficial or helpful thing (e.g., This new phone app is a real boon for posterizing photos.) But many years ago, I remember reading Evangeline Walton's Mabinogian, a tetralogy retelling of the Welsh myth, and encountering the word in a more archaic sense. "I have a boon to ask of ye," was seeking a favor. In the stories, one had to be careful to ask what the nature of the boon was before agreeing to grant it. Once your agreement was spoken, it could not be taken back, but it could prove to be your undoing. Ever since, when anyone says, "Could you do me a favor?" I always say, "Tell me what the favor is, and then I'll decide!"