This is simple, no-cook and absolutely delicious. It's open to lots of variations, depending on budget, personal likes, availability and so forth. There is too much to list so we've just made a few suggestions in the Ingredients section below. Even if you're living on your own, many of these products last for several lunches, sandwiches and the like. Lots of the ingredients will keep for several days in the fridge and many (eg olives in brine) much longer if they're in an airtight container.
Aldi and Lidl are great for cheap olives, jars of antipasti and so forth. At the other end of the spectrum are Waitrose, Ocado and M&S - and everything in between, eg Asda, Morrison's, Tesco and Sainsbury's!
Hunt the salad shelves, free-from chill and shelves and the deli counters as well as the world foods section - it's a treasure trove out there.