Usefulness of Cord Reel with 100-ft Extension Cord
Those cord reels are very useful.  You'll need a BIG one to hold a 100' 12 gauge though.  If you leave 6" or so hanging out one of the big holes on the side, you can wrap it with the end accessible.  

I wrap these with the female end on the spool, so you plug it in first and walk to where you're working.  I guess it works OK either way.  

They make cord reels with receptacles on the spool ...

  

and those work great except when you're working on a ladder.  Sometimes the cord on the tool isn't long enough to reach this thing on the ground.  

When you're working on a ladder it's nice to be able to pull some slack off either end.  This is a pretty good way to go:  



That's from a tip sent into Fine Homebuilding.

The Cordwiz Pro

 

does the same thing as the bucket trick, if you'd rather not do it homemade.  

One other thing to get if you're shopping, a portable GFCI