Bottle of Prime if you're lucky. From a newsagent who will, genuinely, act as if he's doing you the favour.

I was thinking about a pie and a pint

I'd go with your idea. 

Crack.

Do all 3, make a day of it.

sandwich from pret?

Almost enough to make a filling lunch at pret more like

Hand job from a mysterious lady in King's Cross.

Be a mysterious alchy at that price.

How much is a travelcard these days? Is it still about a fiver? 

Put it towards a pint of Peroni

Five blotters of low grade acid.

Down payment on a packet of pork scratchings in a flat roof pub.