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!

Carry as much as you feel comfortable with! Or none at all, if you don't care for it.

Personally, I intend to carry fishing line in my PSK (80-100 lbs test) for lashing, fishing, etc because it takes up very minimal room because 550 cord takes up too much room inside the tin. Then I carry 550 cord too for more robust jobs (tying down tarps, heavy duty lashing, etc).

I found you can stuff quite a bit into an M&M's mini container....


Fold it a couple of times about the length of the container, then start at the bottom and start wrapping it around starting from the bottom (or top, you may need a double wrap and you want to end it at the top). You can get a good 21-25 feet inside the longer one <img src="/images/graemlins/smile.gif" alt="" />