This Brilliant Catering Trick Keeps a Chopped Salad Fresh for Up to 4 Days

[Warpy]

3. Late in the season, when I knew the leaf lettuce would soon bolt

I'd harvest the lot, wash it in a sink full of water, shake all the water off that I could, roll them up a leaf at a time in paper towels and put them into plastic bread bags. The bags would be open for 24 hours,, then loosely closed for another day, then tightly closed. This was before red leaf lettuce and butter crunch and the other varieties were available in health food stores and super markets.

That fragile leaf lettuce would keep for a month. By then, we'd eaten it all and were sick of salad.

It's the same idea as the OP: wet ingredients with paper towels to absorb any water, plastic to protect it from oxygen and from drying out.