Put it in a growler!
I have one small carboy that I use for primary fermentation, and I'm always leaving wort in the kettle simply because it won't fit in the carboy. Tired of dumping perfectly good future beer, I decided to look for a solution today.
I happened to have a growler sitting around, and I just siphoned the rest of the wort into the growler. Pitched some of that yeast I was going to dump after my yeast harvest, and I've got a few found pints from a batch. Sure, it ferments at ambient basement temperature, but I'm all for quick and easy extra beer.