1. I wish I had packed a clock. The clocks in the rooms aren't lighted (unless they've changed to the iPod docks) and are across the room on the desk. With the curtain closed the folks in the bed can't even see it.
Of course the converse of this, I didn't ever need my flat iron, with the sea air, there's no way my hair was going straight!
2. It was never an issue for us, the boy was only 7 on our last cruise so we didn't let him carry his own key. Jillian had her own key, but she usually had pockets too. If you've got a lanyard, I'd bring it for them, but only if they're old enough to do check in/check out on their own.
3. Honestly we've never spent a dime in the arcade. As for placing an amount on their cards, you can't actually do that. Each KTTW card is charged to the stateroom account, and you either have charging priviledges or you don't, you can't set a limit through Disney on a card. Now, given that, you can go to Guest Services and request your statement as much as you want, and the charges for each card are listed separately.