Here are a few essential things I think every dancer should have:
1) Tennis Ball: perfect for rolling out those achy muscles
2) Toe Tape: keep way the pointe shoe blisters
3)Band-aids: never know when a boo boo will occur
4) Theraband: stretchhh
5) Water bottle: have to stay hydrated
6) Emergen-C: perfect little packet full of Vitamin C and energy
7) Nuts: ideal snack to munch on
8) Needle and thread: for sudden wardobe/shoe malfunctions
9) Planner: essential to staying organized
10) Shoes: depending on what style of dancer you are. Personally it's ballet and pointe shoes
11) MukLuks: the perfect shoe to keep your feet warm
12) Small journal/notebook: to take notes/jot down ideas