The juice won't evaporate overnight, but it will run out and absorb into whatever it can touch. Keep the little silicone cap on after filling and it will last months and be fresh.
You might want to look at some of the larger capacity Ecigs, like the Ego-T tank cartridge. It holds 1.1ml. The Ego mega cylinder cart holds 2.5ml. Both of these require that you buy the matching atomizer to use the carts.
An Ego or Riva battery is good for a night out, combined with the tank or the mega cylinder atty and respective cart combination. You can easily get 5-6 hours of vaping off one batt and one or two carts. It doesn't hurt to carry a spare cart with these to make sure. It's always nice to have a cigarette lighter adapter for your charger so you can charge and swap batteries just in case, especially if you use lower mah batts.