In reply to aln:
Well, each to their own of course, but in fact that day we didn't bring any wasabi. Instead, I minced a garlic and a chilli, sliced a few leaves of mint and basil, chopped a couple of well-ripened tomatoes, and mixed the whole lot with the juice of a lemon and a good glug of olive oil. This was poured into a jar and wrapped in a sock.
Later that day, we pulled into Killybegs, the largest commercial fishing port on Ireland's Atlantic coast, hoping to find somewhere to buy the rest of lunch. Worried that we were in for a repeat of the time when we drove through Arborio, Italy, in search of a good risotto, finding only farms and factories and nowhere actually cooking the stuff, our fears were allayed when we found a van at the side of the road selling fresh, perky-fleshed fish, so we got a piece of salmon and a piece of cod, covered it with ice, carried it up the hill, chopped it up a little bit and tossed it with the chilli-lemon-tomato mixture, before spooning it into our mouths with rough chunks of dense brown bread.
Kind of an Italian-Irish ceviche. Would definitely recommend for a lunch on the go.