I'll 2nd the power monkey. Can normally get about 2-3 charges out of mine, and it can charge from pretty much anything with all the kit they give you! :)
During a week long hiking / camping trek I took an extra battery for my phone. I did tend to turn it off duing parts of the day, and also disabled WIfi and data unless I needed it it. At the end I still hadn't used much of the 2nd battery.
I read somewhere that if you are in an area where there is no signal, it is best to switch off, as the phone uses lots of battery searching for a signal.
Perhaps someone will come along to say if this is correct or not.
We got a 150W Power Inverter from Rapid Electronics which plugs into the cigarette socket in the car and converts the power to a traditional 3 pin socket. We charged the phones, airbed pump and electric toothbrush using it over the last few weeks away. Very successful with low battery warning and emergency cut out. As it has a long lead you can also put the inverter and what you are charging out of sight under the car seats. Some have a USB charging point too.
Maplins occasionally have a fairly good solar charger on sale at a reasonably cheap price. 12V output so you can use it with a car adapter. I use mine to run a radio without any problem. Buy on of the usb adapters and you can use it for your iPod etc.
I've just had a look and this might be of interest : http://www.maplin.co.uk/Module.aspx?ModuleNo=348061
on sale until the end of August. This is the 4W output and its cheaper than the 2W at the moment.
I use this one and it works for me: http://www.maplin.co.uk/Module.aspx?ModuleNo=98358
Its a bit smaller than the suitcase job, but neither are huge.