To take advantage of the best prices you will need to prove you are a leisure traveller, en route to the airport, so you will need to give either your flight numbers or your holiday booking reference. I don't think you will need to provide this when you arrive at the station but you may be asked to give them on yr travels from the station to stansted airport.
Going to the airport by train is great, you can take a nap, read (even at night), play a game, or just stare out of the window... The other restriction to buying these cheap train tickets from caledonian 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 child over 5 but under sixteen per adult travelling on the train to stansted airport.
make sure you leave enough time to get to stansted airport early enough to eat, shop etc, so check the times of trains from the station before you go. If you have spare time at stansted airport you can always read or play travel scrabble again! As you have bought your ticket in advance, you don't need to fret about the opening hours of the station.
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