I think the form would depend on where you hand sew and what you sew. I hand sew my repairs on blouses, etc. in the car on trips - actually add lace, put on buttons on the blouses I plan on wearing - that way
I have to do the mending, then that also dictates the size and convenience of the sewing kit. Of course my DH is driving. I update a lot T-shirts this way. I'm thinking a kit that slipped over my window visor would really be a godsend.