I'm hoping / expecting that First MTR will honour the Gold Service vouchers sent out to SWT▸ (South West Trains) season ticket holders. These are one day tickets that can be used anywhere on the SWT network on Fridays, Saturdays and Sundays. I've made the most out of them over the last few years with day trips from Bookham to the South West, often exploring 2 or 3 towns in one day and sometimes using local buses to fill in the gaps between towns.
Although they can be used all year round, I prefer to save them for the summer when the weather is warmer and there are more daylight hours. I will still have quite a few when First take over.