Extension cord (plugs are in short demand and with phones, IPads, camera batteries charging etc, it sucks not being able to charge things.
If you can, bring a small roll on with a case of water onboard. You'll finish the water (unless you want to pay $3.50 per bottle) and use the empty roll on for dirty clothes and stuff you buy.
Alarm clock or digital clock. Nothing like waking up at 3am and having not the slightest clue what time it is.
Lot's more if you'd like