Hi all, this is my first post here.
Not meant as a commercial (I'm not affiliated with them ), but a good recommendation in all honesty.
BackCountry Navigator is an Android (and Windows Mobile) offline GPS app. You can use, for the UK, OS Landranger maps (1:50,000).
It costs 7 GBP but it's well worth it.
Some of the advantages:
* It's totally complete, you don't need anything else.
* It saves you weight.
* As opposed to Google Maps or other maps/navigation apps, it can work offline. Download the maps at home and they're on your phone to stay.
* Afraid of running out of battery? First of all, you can use the GPS in Airplane Mode (if your device doesn't allow that they developed a small fix for that, separate - free - app to download, called GPS Airtime). Secondly, buying a couple of spare phone batteries is much cheaper than dedicated GPS batteries. For most (smart)phones a spare battery shouldn't cost more than 10 GBP. So even if you get 5 or even 10 spare batteries - you're still cheaper out than with a dedicated GPS.
* You can use an old Android phone for this. Personally I use my wife's old Samsung i7500, for which we have 3 batteries. I haven't gone to the limit yet, but with GPS tracking enabled for 2,5 hours I still had 75% of battery left, so I should be able to get 10 hours (or, let's be careful and estimate 7,5 hours) from one battery - meaning three batteries should get me some 22,5 hours of continuous GPS tracking. Seeing that I don't use this all the time when walking as a matter of principle (it's really just for emergencies, for example when forced to walk in the dark or when completely lost / disoriented) - I think I should easily be able to manage for at least a couple of days without any power needed and without having to worry about getting lost.
I'll write some more about the rest of my usual kit elsewhere.