Surfing Waves

I have a 9'4" epoxy board that blew off my car on the highway (note: bungees are not sufficient for highway use...) and miraculously didn't kill anyone or damage anything other than itself. Anyway there are 2 not enormous but still significant gashes in it. Is the best way to repair them to use fiberglass mesh and hardware store resin (west systems or other) or to get Q-cell filler and some UV resin from a surf shop, cut away the flaps and fill it with qcell and resin and then sand it?

Ouch on your behalf; however, next thing you need to be sure of, the composition of the foam.
If it is EPS expanded polystyrene then ordinary resins will dissolve the foam, so sticking with epoxy will be OK!
If the foam is the standard polyurethane then ordinary resins will work, but Imwould still go with epoxy resins to ensureva better bond with the existing resins.
Check too that whatever you do, is compatible right through

Two-part putty, ding dough, etc works great to fill in the gap. Then after you can laminate fiberglass cloth with UV resin.