so i have one of THESE and I love it - It's the definition of easily packable. I also have a classic from Tarpestry.com. these are SUPER awesome, but completely not packable. If I'm going to be running around all day - the matador stays in my fanny pack. if I know i'm camping out for a while, then I'll bring the other blanket. If I'm not using it, it stays in the locker.
pro-tip- if you have a blanket that isn't packable, use THESE to roll it up and attach it to your backpack/fanny pack.