Will you have a car? If so, there's the secret nuclear bunker at Kelvedon Hatch, Duxford's 30 minutes drive away, there's also the DeHavilland Museum near St Albans. I don't have my diary to hand, but if that date is a weekend, the North Weald Airfield museum will be open. There's also a museum in Waltham Abbey. Hanningfield Reservoir is a lovely place to go walking and there's an aviation scrapyard nearby. You could also go walking in Epping Forest.
Any of that interest you?