Is there a good way to store the string so it doesn't lose its twist & I don't have to pack a bow square?

I always just put a twist tie through my string loops when they're off the bow. That keeps them from untwisting.

Take an arrow and hold it with the nock against the riser and make a mark with a magic marker on the arrow where the string is to mark the brace height you want. Now you have a tool to measure brace height and you don't need a bow square.

Trust me, the magic marker mark will not change the "tune" on your arrow. (Before someone asks). 

R