17th Century leather shoe soles excavated in from Woodhouse Farm in 1976

Organic material tends only to survive in extreme conditions of damp, cold or dryness.
Leather, textiles and wood, although found, are not common because they are unstable.
Charcoal is one organic material likely to be discarded on most sites.
Areas believed to contain seeds and pollen can be carefully sampled and studied to see what sort of plants were growing in the local environment.