Bananas have been very popular amongst tennis players for quite a while. I vividly remember Michael Chang going through bunch after bunch on his way to winning the French Open in '89. Bananas are high in potassium, provide sustainable energy, and are quite easily digestible thanks to their mushy texture. That mushy texture provides a challenge for tennis players though - how do you keep bananas from getting all squeezed up in your bag?
This eternal question was answered for me on a rainy evening at a German Christmas market in Dublin, Ireland :) There was a booth exclusively selling "Banana Guards". Any color you can imagine, even ones that glow in the dark. Obviously, I've received a lot of comments about the shape, but hey, they supposedly work for more than 95% of bananas, so they stay in my bag!