Add a spoonful of the frozen concentrate juice (orange juice works best) to your salad and stir. It'll coat all the fruit with the acidity and keep it from browning (and will taste good too!) But your bananas will get soggy. Best to add those last minute.
Today I made a small fruit salad with what I had on hand:
Clementine slices, bananas, and a few mini marshmallows, with a small bit of juice concentrate on it (I used what I have in the freezer - I think it's an apple/passionfruit blend)
Last week I cut up apple, strawberries, tossed in some blueberries and blackberries, plus a spoonful of whatever juice concentrate I have in my freezer. Lasted us 3 days in the fridge and nothing turned brown nor moldy. It may have lasted longer than 3 days, but we'd eaten it all!
Don't forget to add cononut flakes for fun/flavor.