To take advantage of the best prices you will need to prove you are not a business traveller, en route to stansted airport, so you will need to provide either yr flight numbers or your holiday booking reference. I don't think you will need to give this when you arrive at lancaster station but you may be asked to give them on yr journey 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 gaze out of the window... The other caveat to buying these inexpensive train tickets from the station to the airport is that there must be at least two adults travelling together. But another great advantage is that children go free. All children under five go free, and then one kidover five but under 16 per adult travelling by train to the airport.
be sure to leave enough time to get to stansted airport early enough to eat, shop etc, so check the times of trains from lancaster station before you go. If you have spare time at the airport you can always read a book 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 lancaster station.
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