The one thing in your purse you can't live without! (excluding cell phones)

i'm a type 1 diabetic, so i literally cannot live without my meds! :P i carry my insulin, syringes, and all my blood testing supplies with me at all times, in a very cute makeup case. of course, i also carry juice in case my sugar gets low.
 
My keys! I'd say my chapstick, but I use it so much that it now just lives in my pocket. Except for the extra 5 different types that I must have just in case that live in my bag.