Is it worth purchasing a national rail ticket to get the 2for1 benefits in London? I guess I'm wondering what is the minimum I can spend on a national rail ticket to qualify?
Will you be using the tube, bus, DLR and/or trains in London? If so, a travelcard purchased from a rail station (not an underground station) will suffice for the Days Out 2 for 1 discounts and allow you to use those means of transport in the paid for zones. One and seven day travel cards cost the same whether purchased from a rail station or from a tube station, but you must buy from a rail station to qualify for the discounts. I suppose you could buy rail tickets from Waterloo East to Charing Cross and back for £4.40. These should qualify for the two for one discounts during their time span. If you try this, let us know how it turns out.