(First off, apologies for the length and verbosity of this post.  I've been thinking about this for a few weeks, and the questions have been mounting up.  I figured it was best to try put it all into one thread.)

I’m going to be travelling to the UK in 3 months, with my wife and father-in-law, for four weeks.  I’m looking for tips on how to be prepared to make the most of things while I’m over there, especially to do with tech and gadgets.  We’ll be taking our phones (iPhones all round) and an iPad 1.  We probably won’t be taking laptops or digital cameras, though, to keep weight down.

Data & internet access: a lot of the places we’re going should have wifi, but it would be good to have some mobile connectivity while we’re out and about, in terms of texts or minutes to co-ordinate ourselves, and some data to keep in the loop with emails and the wider world.  Data roaming is obviously too expensive, so we’re thinking of getting a SIM card from a local provider for the duration of our trip.  Vodafone.co.uk do a 30-day SIM only plan for 31 pounds, which gives 900 minutes, unlimited texts, and 1GB of data.  This sounds like a good option.  Does anyone have any better alternatives?  Are  there any issues with needing to "unlock" the phone before using a UK SIM card, or is it just "plug 'n' play."  I'd hate to get over there, buy a SIM, and then not have it work...

Photos and video: we’ll probably just use the built-in camera of the iPhone for photos and videos, to avoid lugging round extra devices.  My wife, who is trigger-happy, is worried that she’ll fill up her 32GB iPhone 4S with photos in the first few days.  What are the best options for managing the multimedia flow?  I’m thinking that SkyDrive or Dropbox would be a good option, though the volume of photos she’s thinking about might chew through the 1GB data on the Vodafone plan above.  Short of buying extra data (which I’m not sure about), what are the other options for handling the numbers of photos and video we might produce?  I don’t think there’s any way to download photos to an external storage media without a computer.  Which would mean a trip to a cyber-café with a USB memory stick.  Anyone have an elegant solution to this problem?

Charging: seeing as we’re only taking Apple gear, it’s a bit easier to manage our charging needs.  We’ll be renting a car for most of the trip, so I’ve got a car charger with a USB port, which will let us charge one device as we drive from place to place.  I’m also thinking about getting a third party charger with a UK plug.  I’ve seen one on Trademe which has 4 USB ports – we could then just bring one USB cable for each device, and all charge up our iPhones and iPad at night at the same time.  Or would it be easier to buy a standard travel adaptor, and bring along our usual wall chargers?  Also, for the flights, we’ll be travelling on Emirates all the way (on the A380).  Does anyone know what in-seat facilities there are for charging devices?  I.e. a powered USB port, or a wall socket?  Similarly, what wall adaptors would I need for Dubai and Sydney, where we a staying a couple of nights on each leg of the trip?
Gadgets: are there any essential gadgets for travelling which you recommend?  You know, the things that you wouldn’t do without?

Thanks in advance for your advice.