Sangria esta del Sur: it´s from the south: It´s something you will find in Andalucia, Murcia, Badajoz, but it´s not a drink from the north. On the other hand, the wines in the north are wonderful: La Rioja of course, but the wines from Navarra are just as good and cheaper. If you are on the Ruta de la Plata from Sevilla do try the wines from Badajoz which are ridiculously cheap and have their own uniqueness. Personally, in Galicia I like the (red) Mencias of El Bierzo and Galicia, and as a Philistine still prefer the Ribeiras of Galcia to the much more expensive Albariños...(Well except the really good ones...)
You can always ask for a Tinto de Verano: red wine with Casera, a carbonated (and much sacharined) soda. Una clara is similar but with beer...