To take advantage of the best prices you will need to prove you are a leisure traveller, on the way to stansted airport, so you will need to provide either your flight details or your holiday booking reference. I don't think you will need to give this when you arrive at the station but you may be asked to give them on your travels from the station to the airport.
Going to the airport by train is great, you can take a nap, read a book (even at night), play travel scrabble, or just stare out of the window... The other caveat to buying these inexpensive train tickets from redbridge station to the airport is that there must be at least two grown ups travelling together. But another great benefit is that children go free. All children under five go free, and then one kidover 5 but under 16 per grown up travelling by train to stansted airport.
make sure you leave plenty of time to get to stansted airport early enough to eat, shop etc, so check the times of trains from redbridge station before you go. If you have spare time at the airport you can always read or play a game again! As you have bought your train ticket in advance, you don't need to worry about the opening hours of the station.
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