The way to keep you fresh herb for weeks is to put them in water and cover it with a plastic bag in the fridge… you’ll see, your delicate and fresh aromatic leaves like coriander, mint, basil will stay great this way. Even with thyme which was almost dry, I could resuscitate it to get those purplish flowers back!
If you have a smaller portion just humidify a paper towel and had it to the bottom of your aromatics and close up the container. (see picture)
If you want to keep your salad for long… You must exhale in the plastic bag before closing it up again. A good dose of CO2 goes a long way with lettuce.