An open air snack

We're just about to go to see the local brass band. The title of the event is something like "You bring a sandwich and we'll provide the music". I've bought some bread and things to go in it to make a sandwich. We've got some crisps - well actually they're some sort of healthy pretend crisps made out of soya or peas or some such - and, because my tortillas always sag in the middle, I've bought a tortilla de patatas as well. And, of course, a couple of cans of beer. I can guarantee though that we won't do this "properly". I don't know how many Spanish kids I've seen unwrap their mid morning breakfast, how many women I've seen break out the un-buttered, unoiled rolls in silver paper, how many families I've seen trudging across the sand laden with cool boxes, how many times I've seen tuppers (pronounce that as tapperr) laden with cooked dishes spread out on picnic tables, how many watermelons I've seen carved into...