This is my basic anchor system. It won't work for all cases, but it has worked for me. Originally, I was planning on using some rope I have and buying a few zigzag cleats. I was going to get a carbiner and clip it to the carry handle and run my line through it and tie off on the cleat.
What I ended up doing is getting one zigzag cleat and zig zaging my trolling and anchor lines together in it. I took a caribiner to each handle and ran my rope thru, tying both ends to a small ring for the middle clip point of my anchor. You could also se a heavy key chain loop if you cant get to lowes to get a heavy stainless ring. Chain will work and you can try a thrift store or buy it by the length at lowes or home depot for cheap.
I use a 3.5 lb anchor, but in the river chain probably wont hold you in a decent current seeing as it has nothing to grab with, but maybe going a little heavier with the chains, 5lbs might work.
I had a friend give me a small square piece of lead with a loop on top tha its about 3.5 lbs and it works great for weeded areas. If you can go to cabellas or a sports store, they usually have small folding anchors for 6-7 dollars.