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 give either yr flight details or your holiday booking reference. I don't think you will need to provide this when you arrive at worthing station but you may be asked to provide them on your journey from the station to gatwick airport.
Going to gatwick airport by train is great, you can sleep, read (even at night), play a game, or just stare out of the window... The other restriction to buying these cheap 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 child over five but under sixteen per grown up travelling by train to the airport.
be sure to leave enough time to get to gatwick airport early enough to eat, shop and so on, so check the times of trains from the station before you go. If you end up with 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 fret about the opening hours of worthing station.
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