I have found that the 6" square is a little large. So I have found some small scrap wood that has square corners for when I am setting the ribs in the wings. Most fit tight and stay set but for the loose ones I uses these squares.
Sanding blocks from scrap wood work great.
Don't go crazy until you start building and you will figure the little tools that "you" like to use.

Good Luck and Happy Building, I feel that is the best part of the hobby. </p>