Benfleet rail station (0900 from Fenchurch Street or 0936 from Southend Central; car drivers can park at Stanford-le-Hope rail station SS17 0JX (or the cheaper King Street c.p, SS17 0HL) and take the 0931 to Benfleet.)
A Thames Estuary walk from Benfleet to Stanford-le-Hope, mostly using the England Coast Path but with an excursion on permissive paths into the Bowers Marshes. Finish: Stanford-le-Hope rail station. Trains back every half-hour
General Notes
Bring your own packed lunch etc - the lunch stop is likely to be huddled against the sea wall sheltering from a chilly wind somewhere north of the Coryton oil terminal. Top tip: if you're taking the train from the Southend direction, buy a return to Stanford-le-Hope. No need to register in advance