Milk
Powdered or plastic UHT milk in those vile little pots do not do anything to improve the taste.
For those lucky enough to travel in Club, or higher, ask for some real milk it does make a difference. - economy I'm afraid you have next to no chance as the penny pinchers at BA recently cut back the milk allowance to one pint (per return journey) on some routes so Pursers and CSDs will be reluctant to give up their crew milk for pax if too many ask for it!!
Bad show BA on the milk and coffee front I'm afraid !!!