The best of the backyard (tomato, egg, bell pepper), farmers market (lettuce, green beans, potato) and . . . Trader Joe's (tuna, capers, olives, mustard). You could do worse than TJ's for those four ingredients. You could do much better, but you could do worse.
And the canola oil for the dressing--the good stuff brought back from a trip to Sweden. So clean, and so strange higher end canola/rape seed oils aren't available locally. Salad oil. It doesn't have to come from olives.