I usually carry about 50ft, although a 100ft maybe even better. I have used it for the obvious, shelters and such. I have also used it in the winter to pull down dead limbs off of trees for a fire when there was several feet of snow on the ground, making collecting wood impossible by the normal means.
I have used it to dip for water when the only water was in a stream with a steep bank and no easy way down. I just tied my water bottle with the top off to the cord and let it down until I scooped up enough water. I then dumped the water into another bottle and repeated this until I had all the water I could get.
There are many uses for cord in the wilderness. Making repairs, bootlaces, bundles, you name it!. You can also take the inner lines out and make gill nets, lighter string, whatever.
I have never needed more than 50ft, but usually travel with other folks that keep about the same amount with them. So, you be the judge. Cheers!