Here is a 20% discount off family and friends railcard. I have purchased a two together as my mum and I have travelled a number of times and makes it so worthwhile. We travelled 1st class from Newark Northgate to London Kings Cross for only £36 for 2 of us. It was on a Friday so got free alcoholic drinks and foods.
You get points for booking your trains this can be converted to money off future train journeys. I signed up as they had bonus points which was equal to £5.00 off