I just wanted to clarify that you are working off of current information about 2 for 1 offers. I know that there was a change in the past year or so where some of the tickets or passes that formerly would make one eligible for these offers no longer worked.
I cut and pasted this from the National Rail website about which tickets work for these promotions and which ones do not.
Is my ticket valid for 2FOR1?
YES! The following ticket types are valid for 2FOR1 and other offers on daysoutguide.co.uk:
National Rail orange paper tickets including:
Travelcards - purchased from a National Rail station only
Print @ Home or Mobile tickets (m-Tickets) for travel on National Rail services (showing the National Rail symbol)
Annual Gold Cards
Gold Record Cards (when an Annual Season ticket is held on smartcard)
Train company issued smartcards (e.g. The Key, c2c Smart)
NO! The following ticket types are cannot be used for 2FOR1 and other offers on daysoutguide.co.uk:
Transport for London (TfL) issued Travelcards, including Travelcards bought on visitorshop.tfl.gov.uk
Contactless payment cards or mobile payments
Heathrow Express and Heathrow Connect tickets
Stansted Express and Gatwick Express in-flight or mobile tickets where the National Rail logo is not shown
If you are making a one way journey or your ticket is valid for one day, you can use your National Rail tickets and offer vouchers only on the day of travel.
If you are making a return journey, you can use your National Rail tickets and offer vouchers any day on or between your outward and return journeys. For example, if you arrived on Thursday and will return on Sunday, your tickets will be considered valid for the offers on Thursday, Friday, Saturday and Sunday