You could get the train to Lyndhurst and do a route in New Forest one day (just about big enough to do a 40 mile round trip in), camp there for the night, and the next day cycle along the seafront and over the ferry to the Purbecks (stop in Swanage for fish and chips) and camp there that night, then the next morning get the train back from Wareham or Weymouth. Nice places to cycle - some parts of the Purbecks might be a little hilly if you're carrying a tent fixed-gear though.
You could get the train to Lyndhurst and do a route in New Forest one day (just about big enough to do a 40 mile round trip in), camp there for the night, and the next day cycle along the seafront and over the ferry to the Purbecks (stop in Swanage for fish and chips) and camp there that night, then the next morning get the train back from Wareham or Weymouth. Nice places to cycle - some parts of the Purbecks might be a little hilly if you're carrying a tent fixed-gear though.