From an interview with Iain Sinclair, who’s probably one of the UK’s best prose writers:
The way to explore London’s territory initially was walking, which involved a burden of other people’s knowledge. So the rucksack represents this unread mass of material. Not just fictions, but testaments, documentation, statistics, obliterated council papers, adverts – more than you could manage. Working and walking and reading became completely interwoven. Walking is a form of reading, in the same way you can read a painting, or landscape. Therefore a journey is a form of turning the city into a film, or a book.