A theoretical shailo. One who is making a bris the day after shmini etzeres on isro chag (in eretz yisrael) and will have limited time to cook may they prepare the food already on chol hamoed for after the moed? I have heard poskim that are matir this because it's being done for a mitzvah however I'd like to find some sources for this or those that discuss this.
The Shu"t Shraga He'maor (2:48 Ois 2) deals with this exact case, and permits it on the grounds that it is for the sake of a mitzvah, and if we would require him to purchase everything ready made he would lose money. However Rabbi Y. Farkash in Chol Hamoed Kehilchoso (pg. 238 footnote 38) writes that this heter is not so clear; see there.