I'd suggest that before you start thinking about models of smartphones or tablets, you check what sort of data signal you get in your woods and whether it's going to be good enough for the type of thing you might do. This is going to vary between the four networks depending on their coverage in your area. You could try working out from their coverage map or coverage checker what sort of signal you'll get, although I'd probably want to invite a friend with a smartphone or tablet and see how good it is in real use. Here's the coverage checker for the O2 network -
http://www.o2.co.uk/coveragechecker. The other networks are I think EE (includes Orange and T-Mobile), Vodafone and 3. There are many other companies selling contracts that utilise these four networks.
I find for example that in my woods, my phone will just about manage to slowly trickle email back and forth while it's in my pocket or the car. Attempting to use the web or anything else where higher speeds of data are needed for practical use is painfully slow and often sees timeouts that make it almost useless.
Most tablets currently available don't allow voice calls to be made and received, although there are some on the market that do such as the ASUS Fonepad -
http://www.pcpro.co.uk/blogs/2013/02/25/asus-fonepad-review-first-look/Most if not all smartphones and tablets will allow you to take photos and video. I find that with my Samsung Galaxy III, they look OK when viewed on the handset itself, but transfer to a PC and start blowing them up or printing them and they can start to be a little disppointing. So, yes, great to have as it's always in my pocket but if I know in advance that I want to record some imagery then I'd pack my stills camera or my video camera.
Watching TV live or streaming any other video is going to place heavy demands on your data connection and there are two issues you might consider. First, is my signal good enough (see earlier), and second, is it going to be expensive on my contract? Alternatively, you could consider having stuff to watch pre-loaded onto your device (prepare at home to watch in woods) - where options might include downloading stuff with BBC iPlayer, ripping DVDs, stuff you've recorded at home with a PVR etc. A different solution for live TV could be a laptop with a plug-in Freeview receiver and portable aerial.
