we bought so stuff sacks from millets to put our clothes in for the walk, and i also used a bag which i lined my rucksac with from millets, bright orange in colour, and very sturdy - cost about 3 quid. was very grateful that i did when it was persisiting down on the penine way!
we also bought some small washbags from tesco, £1 each, which were handy for keeping small stuff like first aid kit and wash stuff together and dry