Keep extra hair ties on your keychain
Get anti-chlorine shampoo or use ketchup to counteract swimming pool green hair phenomenon
Forgo mascara in lieu of lash extensions as mascara will surely run in humidity and ruin your look
Make sure you have foundation with SPF in it for a one-two punch. Also, buy a shade darker than your normal foundation to reflect any color you get from summer sun.
Keep extra dry shampoo and deodorant in your glove compartment.
Use Kiss My Brass shampoo additive to eradicate brassy tones from the sun and saltwater.