A 10 lb. mushroom anchor will do a fair job of keeping the boat where you left it, if it's not very windy or rough water. I use it to keep the boat near shore when launching at Lind Coulee, or keep it beached when I gotta do that.  The nice thing about the 'shroom anchor is that it doesn't tear up the boat as a fluted anchor could. I put it in a plastic paint bucket in the battery/gas compartment, along with the 30' or so of 5/16" poly rope.

I've left my boat near the mouth of Schlaegle Bay, anchored the bow into the prevailing breeze, and stuck the skeg into the sand, locked it all up, and waded into the bay for some fishing, carrying just one rod, and a few items in a fanny pack. Nicer to get the boat in, but there wasn't enough water that morning. Be sure to block the entrance with the boat enough to keep somebody from zinging in there on power. You won't like that, especially if you're standing on the sandbar & fishing the lillypads at the entrance! C&R, Steve