I don't have a yak but I use an 8 pound mushroom anchor on my 15' canoe and it holds well by itself. I also have a second anchor, I have one at each end, so I can remain steady no matter which way the wind blows. It's about 10 pounds made from a bleach jug filled with concrete.
I've seen people talking about using a piece of PVC pipe, capped on both ends, with re-bar at right angles through it. They travel with it empty and fill it with sand or rocks at their fishing hole. I plan on trying a version of this without the re-bar for my float tube this year.