- Unlocked GSM cell phone. In most places overseas, you can pick up a pre-paid SIM, and the convenience often outweighs the cost. My rule of thumb has been a two week minimum stay if it requires any effort. If you really like your GSM phone, you can unlock it so you don't have a learn a new phone interface. I was able to get my HTC Aria unlocked by the folks at freeyourhtc.com (Quality Product Source). I think you can find cheaper unlock codes on ebay.
- Capital One credit card (or credit card that doesn't charge international fees). Make sure you pay it off monthly as the rates are horrible.
- Spare passport photos. This one is a bit less important, but some places require passport photos for the simplest of things - like getting a SIM card in India. Far easier to get them done ahead of time.
(removed HSBC account, which charges 3% on non-Premier accounts.)