Along the Camino de Santiago, and more specifically the French Way you will constantly be passing villages, with stores and bars and restaurants, so you will never starve.
One option that you may consider is to stop by at the supermarket. There you can get any kind of food. Bread in Spain is one of the basic foods, and they sell really good quality baguettes and other types of breads at the supermarkets as well. You can buy meat or cheese and ask the worker to make you a sandwich with the bread you are buying.
It is also a good opportunity to check all the meat section (Jamon Serrano/Chorizos/Salchichon/Pates…), which is quite big compared to supermarkets in North America.
Alcoholic drinks are sold in supermarkets, so you might find beers and bottles of wine for a really good price.
In Sarria you can go to:
Supermercados en Sarria ( Lugo ) – Calvo Sotelo, 128-130
CRISTO ALIMENTACION S.L.
Supermercados en Sarria ( Lugo ) – Diego Pazos, 45-47
Supermercados en Sarria ( Lugo ) – Matías López, 108