A great list for GFCF Halloween candy is at http://www.gfcfdiet.com/Chocolatecandy.htm
I always go through our candy after trick-or-treating and trade out the stuff my kids can’t have with stuff they can have. My kids also will go for cool stickers, etc. instead of candy for some of the pieces. It’s what we do every time we are faced with the “big bag of sugar” (Valentines bag from school, birthday party bags, etc.) so my kids know it’s the deal. They like that they get to see what they are getting right away. I remember wanting to sort out and trade stuff with my sister when I was little too!