Which side are you going to? Kona or Hilo?
If you go to the Kona side, you HAVE to go down the main road and spell your name on the side of the road in white coral. It's just something you HAVE to do!!
There's really not a whole lot to do there. Lots of pricey touristy stuff.
If you are into adventure, I suggest doing the Manta Ray snorkel. It's awesome and breathtaking!
I did manage to hit a couple Coffee Farms, but didn't get to any quilt shops there. Wasn't really there for that (gasp!) since I was living on Oahu at the time and could get what I needed there.