Bring waterproof container for personal items like mobile phone, wallet, purse, keys... (Hucket Bucket works great and serves as a seat between games)
Bug spray
Sunscreen
Aloe (in case you forgot to use sunscreen)
Trash bags to store your cleats, sweaty and/or muddy clothing in trunk during travel to hotel between tournament days and on the way home.
Covering to protect your vehicle's seats, floors and trunk area from wet or muddy clothes/shoes during travel to hotel between tournament days and on the way home.
Newspaper to stuff inside player's cleats at the conclusion of play each day.