If it's a Devon and Cornwall Gold Card then you get 34% off Cheap Day Returns and Savers within Devon and Cornwall, another adult travelling with you gets the same discount, and you can take up to four children for ^1 each.
I used it this weekend to take three bored children and myself from Newton Abbot to Dawlish and it cost ^2 return - I think that's a good "added feature" of my season ticket for sure.