Maps

I always take a paper Ordnance Survey map with me when I go on a walk...except for very local walks. I use the 1:25,000 scale for the Peak District and 1:50,000 for elsewhere. The Peak District maps are very good; in particular there are two features I find very useful, field boundaries are shown and you can usually tell which side of a fence, wall, or hedge a path goes. The only thing they lack for me is the location of bus stops out in the rural areas.

The 1:50,000 maps aren't as detailed, lacking the two features I've already mentioned. Ordnance Survey only produces the larger scale maps covering the areas of the national parks though.

Of course, when planning a walk I use online zoomable maps.