Am I the only one who carries little or no para cord? I just read where one hiker carries 100' - just in case.  I'd rather use the space/$/ weight in  my pack for other items... 
Cordage is one of the most useful things in a TSHTF. And one of the most difficult to improvise/manufacture. At least in the short term. Not having any strikes me as being unwise. 
2 x 20' lengths in my back pocket's. 
1 x 30' length in my bag or back pack (minimum)
And I might have at least one more 3-6' length stashed somewhere about my person.
So as you see, 100'is not unreasonable. 
One thing that I do like about 550 cord is that it is very user friendly. Easy to knot and easy to undo.