Long time lurker - first time poster so be gentle :)
Was stuck for power this afternoon whilst out and about and happened to stumble across this Texet power bank in Wilkos for £8.
I know there's loads of these kicking about cheap on ebay but this seems decent quality and IMO very good for the price.
I also found a curly lightning cable in the car section for £2.75 got the 2 and it juiced up my iPhone 5 from 11% to 60% over lunch and that was just out the box!
Thought I'd share anyway, the lightning cable is a bargain itself!