Any tips on keeping cut salad fresh?

I work full time and live alone, so I try to meal plan in advance. I LOVE salad and often cut as a basic, lettuce, onion, cucumber, tomato’s and sweetcorn to last for two days, so I can just fix it straight onto my plate when I’m ready to eat.

Only do two days worth as it starts to go brown.

Any tips on how to make cut salad last longer!

For background, I wash all salad, dry in my salad spinner, cut, then transfer into a large plastic mixing bowl, cover the top with cling film (directly on the salad) and then put a plate over it.