I'm a bit cough about lists so I have a trip checklist on my laptop that I refer to for each trip. Many of the things have already been pointed out by others. Some extra ones are:
. Find out about required innoculations needed for the country/countries travelling to and get them done well in advance.
. Arrange travel insurance. The old adage is if you can't afford insurance, you can't afford to travel.
. Prepare an exchange rate "cheat sheet" for each adult travelling member. Helps a lot with shopping.
. If you are taking medication for any conditions, get a letter from your doctor in case customs want to take them off you or they thing they are illicit drugs.
. Check out what sorts of power adaptors are needed for where you are travelling and take them. The power board is also a good idea so you can charge multiple cameras, MP3 players, phones, computers, tablets, etc. For her hair dryer, ensure the adaptor can handle the draw without blowing a fuse.
. Remember insect repellant for some countries - and suntan cream.
. Ensure webmail is working with plenty of available quota.
. Understand what visa fee or departure tax is payable for the location and currency required.
. Apart from passport copies, ensure you have copies (electronic and/or paper) of visas, travel insurance certificates and PDS, E-tickets, credit/debit cards.
. Arrange pre-payment or D/D payment of any bills that may come in while away.
. International roaming set up on phone, plus understand what settings are needed to avoid international phone/data roaming charges. Using free wifi zones and calling via Skype, or doing your Facebook on wifi only will save heaps. There are also smartphone apps for texting over wifi I think.
. Check out Trip Advisor forums for where you are going for things to do, places to eat.
. If you have a monitored security system, ensure the list of numbers to call is altered so someone responsible can takes any calls for you.
. Put a "No Junk Mail" sticker on your letter box. But just in case, ask a trusted neighbour to clear any that appears.
. Take photos of any expensive equipment you are taking with you (cameras, computers, etc) including the serial numbers, and upload these to the net or USB stick where you can access them while away in case they are stolen.
. Pack a torch - better than the smartphone "Light" when walking dark streets.
. Notify banks that you are going away and where so that they don't put a hold on your card when used in that country.
. Ensure that any external sheds are locked and valuable outside items secured.
. Turn off laundry and kitchen taps (if possible) so nothing bursts while away.
. Register with smartraveller.gov.au so they know where you are if something happens (tsunami, earthquake, uprising, etc). I know some will say "no way" - up to you.
So they are my additions to this discussion. Hope they help.