Sewing is very useful. I hardly know jack about the specifics, but if you can whip stitch, you can sew on a button, and do some basic mending and joining. If you know another kind of stitch (I don't know the name), even if it isn't a really consistent stitch, you can mend, repair, and create in many fabrics (assuming it's not a knit or something that needs special stitching or cutting according to something called a bias).

Right now I actually have a small project in progress: My girlfriend bought a small crossbow pistol for some back yard target shooting, and she needs a way to carry the bolts. I happen to have a worn out pair of jeans, so I'm making the end of a leg into a divided pouch with a button closure and strap loops to accommodate different types of slings or belt mounts.

Two kinds of stitches.