I spied this on Pinterest a while back and finally tried it about a month ago. I am pleased to tell you that THIS REALLY WORKS!
So I buy bananas at least once a week. And it doesn't matter if I buy them as green as an apple, within two days, they all have brown spots. And then the next day, they are really only good for smoothies and banana bread (which I make about once a year).
But this tip is so easy, pretty much free, and really, truly extends the happy period of your bananas.
Start with a bunch of bananas.
Take a small piece of tin foil. It doesn't matter which side (shiny vs. matte) is up or down.
Wrap foil around the top portion of banana bunch. Each time you pick off a banana, tighten the foil cap. (I reuse this foil many times over so really there is very little waste.)
And there you have it. Happy bananas. That will extend the "good" period by several days. I have no idea why it works (my guess is something to do with oxygen and other science-y business) and don't care. It does. I just works. And that's pretty much all I need to know.