The OS maps should be a staple in the journey pack for all adventurers and outdoors-types. This particular map is also an essential if you want to do any exploring around the beautiful South Downs. All the major walking and cycling routes are earmarked here. Dump your apps and get back to basics; phones won't be able to help you navigate when the zombie apocalypse hits :P
Possibly the most comprehensive mapping in the world that is available to the general public. With such detail, information and user interpretation who could fail to rate it anything less than 5 stars?