We used to just have a kind of permanent smorgasboard of deli stuff in the summers, and we would make our own sandwiches.
There was usually sliced meat of some kind (ham, salami, bologna etc) and sliced cheese. (That would all be bought at the supermarket deli counter, presliced, as was the bread). Then we would slice up a tomato or two, wash a couple of leaves of lettuce per person and set out various condiments (generally mayo, mustard and gherkins).
Occasionally my mum would make tuna salad and we'd all have tuna melts, or chicken salad/coronation chicken.
We would usually have a handful of something crunchy as well - cherry tomatoes, carrot sticks, tortilla chips, pretzels...
By the time we were your DS's age we would be responsible for setting out the food ourselves and make our own sandwiches (and generally run away with them, lunch wasn't a sit down together meal like dinner). Not sure how your 3yo and baby will cope but at least that takes one out of the picture?