A.B.
I went to a 3 year old party indoors. The kids had a playdough table which they liked and there were also some toys and a station to decorate butterflys (on construction paper with sticks) or bumblebees. That was cute. My son is a wild one though so he was making a mess of the glue and I had to control him. I think simple is best. You don't need to plan games.
Hope the weather is good! I think hot dogs are fine. Sorry don't know about GF foods.