"comida para llevar" establishment
I personally think Mercadona isn't the best place to get "ready to eat" meals. Simply search a "comida para llevar" establishment, and you will found where local people in each neighbourhood get it. Preferible if this food shop is near a fresh market "Meccado municipal" or "mercado central". this is a way to promote local business, that is even better than use great corporations as Mercadona