Avocado "ice cubes" have become my favorite secret smoothie ingredient. They make smoothies creamy and delicious (not to mention healthy), they're super convenient, and they are a perfect way to preserve avocados at their peak ripeness.
When I have a ripe avocado that I don't need for anything else, I will mash it up and spread it into an ice cube tray (you can also just scoop spoonfuls onto a plate if you don't have an ice cube tray). After freezing overnight, I use a knife to pop the "ice cubes" out of the tray, store them in a freezer bag, and voila--the perfect addition to any smoothie! When avocados are on sale, I will stock up now because I don't have to worry about them going to waste.
Once I came up with this idea, I was upset that I hadn't been doing it for years! Enjoy!