Another vote for the Etrex 20 which I bought after my first C2C.
On my first C2C I got to the top of Greenup Edge after Borrowdale and was in the mist and couldn't see any paths. I didn't want to go the wrong way, especially on my own so had a rest and waited about 10 mins till the group behind me caught up then I followed them at a distance until the mist was gone. At that point I decided to get a GPS and I've used it ever since, clips nicely onto my backpack strap loop.
On my first C2C I had the Harvey maps and a wainwright guide book. I found the Harvey maps to not show enough detail but the guide book obviously was more "zoomed in" and showed the path clearly.
I put the guide book in a sandwich bag, kept the rain out plus it kept the page for me so I didn't have to keep opening up the book and searching.