One of the ways I like to either finish up a tube of paint, use up colour I don't particularly care for, or use leftover paint from my palette is to apply it to fresh canvases as a base for future paintings. There are times I apply it with a roller or paintbrush and leave it, and other times when I like to spray the paint with a ton of water, allow it to sit and then move the canvas around to manipulate the paint or mop up the excess with rags to create patterns. I tend to like to use up paint fairly quickly as I don't like waste...and I really, really enjoy 'fresh' acrylics.
It's fun to see what happens while they sit. Then, after quite a large block of time for drying, I continue to add colour and pattern. This is where I can cover those blocks that don't interest me and where I can see how the previous colour, which I may not have liked initially, allows the layers above it to pop. I also find that squeezing the colour directly onto the canvas makes the work more playful, plus I don't have a palette to clean at the end of the session. A big bonus.
Oh...and I have also learned, if I don't want to dip my paintbrushes into my drinks unintentionally, be sure to pour my drinks into closed containers ;)