Buy supplies from the several groceries (especially Abarrotes Oasis, in front of the Cathedral) along main street Independencia or the town market on the plaza, west of the cathedral. As for restaurants, the steady flow of pilgrims supports several near the plaza.
For a snack right on the plaza, the Pizzería San Miguel (Independencia, next to Hotel Plaza, 8 a.m.–9 p.m. daily, $3–10) puts out good pizza and sandwiches.
Next door, second-floor Restaurant El Campanario (tel. 388/385-1370, noon–7 p.m. daily, 8 a.m.–9 p.m. daily during fiestas) serves from a broader menu of breakfasts ($3), lunches ($3–4), and dinners ($3–7), while also affording an airy, upstairs view of the plaza.
Get a bit of graceful colonial-era atmosphere with your seafood, tacos, or hamburguesas ($3–8) at the old mansion, now El Molino Rojo (Red Mill) restaurant. Find it on the main street, by the HSBC bank, a block west of the plaza.
Equally serious eaters head the opposite direction—east to the end of the main street and downhill three short blocks farther (two downhill, one left) to 
Restaurant Campiña del Herrador (23 de Junio, across from Hotel Pedregal, tel. 388/385-0376, 8 a.m.–10 p.m. daily, $3–10) for hearty country-style breakfasts, lunches, and dinners.