This time they were giving my parking neighbor, the Camper with slideout, hell on wheels for fruit, vegetables, meat, eggs and a battery powered chainsaw. I had stopped to presta el bano. I was not red lighted but I noted every last pickup, van and RV was being waved over to Aduana secundaria. The driver was mad as hell. Looked to be about 150 dollars worth of groceries sitting on the ground. He was headed to Bahia Concepcion. Other rigs had groceries sitting on the ground.
I just got through touring Soriana, Commercial Mexicana Sams Walmart, et al. Parking with a small car is wsy. An RV is about as parkable as an aircraft carrier Ensenada transpeninsular.
La Bodega in Sn Quintin is wide open with 99.99999999999% less traffic than the nightmare of Ensenada - El Cipres.
When I first started coming to Mexico I knew not a word of Spanish. Those were the days when going shopping meant a tienda where the stock you wish was behind the counter and a person had to ask the cajero to fetch it. I was not discourged or defeated in asking. Are RV'ers today stupid? You sure make it sound like they are.
Grab a cart and tour the store. Put things you like into the basket and leave things you don't like on the shelf. It takes no longer to shop Mexico than it does the USA. I did both the last four days. I asked zero questions in Ingles ni Espanol.
Remember the OP is going to concentrate solely on things he cannot bring into Mexico, not for condiments, box and canned food.
How hard can it be?