The common ingredients used for tapas are usually more economical cuts of meat (almost always pork, more on that in a minute), seafood and preserved products like olives, anchovies, etc.
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A note on the incredible amount of pork eaten in Spain: It is literally everywhere. Entire shops are devoted to Jamon, with hundreds of hams hanging from the ceiling. Even regular supermarkets carry 5 or 6 different types of Jamon. This tradition developed for a very real and serious reason, according to The Cambridge World History of Food:
"Spanish enthusiasm for pig meat stems in part from pork’s past importance as a symbol of cultural identity. Because Moors and Jews did not eat it, Christians saw the meat as more than simple nutrition. In sixteenth-century Spain, pork eating was an acid test faced by Spanish Moriscos and Marranos who publicly claimed conversion to Christianity. Conspicuous pork avoidance could result in an appearance before the tribunals of the Inquisition."
—The Cambridge World History of Food (www.cambridge.org/us/books/kiple/hogs.htm)
So you have to eat your pork! As my readers (both of you?) already know, fortunately for me, I am already a huge pork fan! So the Inquisition will have to find another reason to come after me (shouldn't be too difficult)