In one of my previous lives it was my task to actually encourage the Ops department regarding maximum fuel CFP's and tankering fuel.
A couple of prime examples, for one season we weekly had a B757 positioning in from LTN (where the fuel cost index was 86%) to CWL (where the fuel cost index was 100%) to operate a CWL/LCA (a 4.5 hour sector), to tanker fuel in from LTN would cost around 4% so, weekly, on a 4.5 hour sector we could save 10% on the fuel.
Another prime example was CWL/KLX, once weekly where CWL was 100% and KLX a staggering 151%.
As has already been suggested, if an airline is top be truly green then cease flogging duty frees and cuddly toys, forbid any excess baggage, all cargo needs to go by surface transport, strip the paint off and go naked fuselage las do AA etc. etc. etc.