Q. I believe it is a minhag to eat mezzonos at a kiddush, especially if you’re not drinking the kiddush, before eating other food.  However, I’m sensitive to grape juice, wine and alcohol so I rarely drink at the shul kiddush.

I’m also sensitive to grains so I sometimes bring by own snack which requires a mezzonos bracha. Is that sufficient or is it not even necessary?

A. Shulchan Aruch (O.H. 273: 1) rules that kiddush has to be recited in the same place where the meal is going to be eaten.
Mishna Berura (ibid 25) that any mezzonos are qualified as a meal. One should eat a Kezais or olive volume of the mezzonos (about 28 – 30 gms.).

Rabbi A. Bartfeld as revised by, Horav Dovid Pam, Horav Aharon Miller, Horav Chanoch Ehrentreu and Horav Kalman Ochs Shlit’a