Someone mentioned this video I made awhile back, so I thought I'd post it up again.
For lack of a better name, I call this the "The Rolling Slippery Double Half Hitch", or as my kids refer to it, "the loopy thingy".
My Dad taught me this method of tying this knot/hitch when I was a boy. It's a very fast and secure knot.
The video starts out showing it tied to a post in normal time. I use this hitch for so many things it's hard to list them. Tarp tie-downs, ridge lines, securing the neck of tote bags, the beginning of pole lashings, fire wood bundles.... It's uses are only limited by your imagination.
I'm going to throw in the Power Cinch knot in this same post. I also use this constantly for tying down loads, the business end of ridge lines, in place of a "taught line hitch" for tent/tarp tie-downs, clothes lines, you name it. You'll see the rolling half hitches come into play in this second video, also.
Between these two knots, I get 90% of my needs met. I'm a firm believer in "slippery" knots. I've done most of my camping in places where the lines were usually wet.