It's not like the "Old Days" today, merchants access the SAT/SHCP website every morning with their Smart Phone, and know the tipo de cambio as they are sipping cafe and eating their pan dulce. Most of the foodstuffs now, a majority are imported so don't look for "no icreases" on even basic commodity food stuffs.
I fully expect Petroleos Mexicanos to lump-sum increase the price across the board for comistibles, around 110%. They've done it in the middle of recessions and depressions and they'll keep doing it.
The key to a sagging tipo de cambio is capital flight. Billions of pesos are flapping northbound to Texas. The wealthy and the government base everything on the US dollar regardless of the price in M.N.
If this all sounds a little nuts, remember the economic mantra of the Mexican businessman "When Business Slows, Raise Prices!"