As a girls team coach for almost a decade, let me share these items that were always in my coach's bag :

[1] Complete first aid kit (Johnson&Johnson $20 type)
[2] Chemical ice packs
[3] Hair ties
[4] Extra jerseys, shorts, socks
[5] Extra towels (dry to start)
[6] Advil/tylenol
[7] Extra copies of directions between fields
[8] Extra copies of schedules
[9] Extra case of water
[10] Jumper cables (for parents cars in the parking lot)
[11] Headbands
[12] Sun screen
[13] Lip balm (multiple tubes)

On the food front, we always found that a couple dozen bananas along with a dozen oranges were good to replenish nutrients in the two hour breaks between matches.