Poly is also not very good at holding knots.
I carry 100m of 3/8" 3 strand line, and use a danforth style anchor with around 4.5m of chain. Depending on your coast you might be able to go for less line, but as our shores can drop quickly and the anchor is a safety device I prefer to have more than less for staying from shore breaks. Bruce anchors works great for many substrates.
Some will mention the folding grapnel anchor. Many of us are completely against them, unless you NEVER plan to the leave the boat while it is in use.
How you attach to the boat may or may not be important too. I quickly made up a bridle to disperse the load on the d-rings.
My anchor crate setup. The milk style crate works awesome as it vents, and holds the anchor in place. My new one also has a mount for the bow light, and bungee mounts sewn on to mount it in the boat.