As I was standing in Pump yesterday, a girl went to tie her lovely long hair into a ponytail, only for the band to snap and go flying a couple of metres towards the barbell rack. Luckily, nobody lost an eye and she had another one looped around her water bottle.
RESOURCEFULNESS!
I was deeply impressed. I always have one looped around my water bottle and another around my gloves.
Don't give yourself any reason to skip 
a) your workout
b) the intensity or duration of the workout you planned

Here's my tips to be prepared.

• Keep roll-on deodorant in the glovebox (Dove @ Chemist Warehouse)
• Keep a headband and snag-free elastics in your handbag (Gliders @ The Beauty Office) Under $5!
• Have a towel, change of underwear, t-shirt, shorts and socks in a gym bag in your boot (Ankle socks $4.95 @ Cotton On Body, Barrel Bag $10 @ Cotton On Body)
• Keep some face wipes in your glovebox to remove makeup before the workout and that sweaty 'glow' afterwards! (Yes To Cucumbers Facial Wipes $4.99)