To take advantage of the best prices you will need to prove you are a leisure traveller, on the way to the 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 provide them on your travels from norwich station to the airport.
Going to the airport by train is great, you can sleep, read a book (even at night), play a game, or just gaze out of the window... The other caveat to buying these cheap train tickets from the station to luton airport is that there must be at least two adults travelling together. But another great advantage is that kids go free. All kids under 5 go free, and then one child over five but under sixteen per adult travelling on the train to luton airport.
make sure you leave plenty of time to get to luton airport early enough to eat, shop and so on, so check the times of trains from norwich station before you go. If you have time to kill 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 norwich station.
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