That's exactly what we do: form half a plan for a day trip the night before, then wake up the next morning, see how we feel and what the weather's like, and if everything's conducive to a nice day out we jump on a train and off we go. Did that over the bank holiday weekend just gone for a day trip to Broadstairs, and lovely it was too. We never go on holidays but enjoy a few such short-notice day trips a year.
There is, admittedly, Southern's money back (née rainy day) guarantee which can help in situations like this if you need to order tickets online (e.g. if the ticket office will be closed and the machines don't sell the tickets you want), but it's still a bit of a faff arranging a refund.
There is, admittedly, Southern's money back (née rainy day) guarantee which can help in situations like this if you need to order tickets online (e.g. if the ticket office will be closed and the machines don't sell the tickets you want), but it's still a bit of a faff arranging a refund.