One hundred yards of high quality nylon sidewall string.  Sidewall string is slightly thicker than crosslace.  Sidewall is used to connect mesh to the plastic of a lacrosse head.  Additionally, most stringers use sidewall to string the topstring of a stick.  The top is strung by doubling up sidewall string.  If you are new to stringing, sidewall is something you will definitely need.

A Note to Stick Doctors: Don't be fooled by other vendors that use materials other than nylon. Nylon is far more reliable, ask any experienced stick doctor. If it's not nylon, don't use it. Other sidewall constructions wear very quickly, the last thing any player needs is a torn sidewall in the middle of a game.