I often find holes wear in my jeans between the legs, so I patch them with fabric on the inside and lots of rows of zig-zag sewing.
It's not a very visible spot so it does not have to be perfect, but it definitely increases the useable life of the jeans considerably.
Def trying this next time my jeans get a hole there! I've thrown away so many pairs because I didn't think it was repairable D:
You can also do the patch before the hole actually wears through - even just stitching over the top of the thinning area is probably enough to provide extra reinforcement to stop the hole forming, although the extra fabric provides a more stable base for the new stitching.