Yellow card

From Frikipedia

Scroungy student method to obtain even further discounts on their beer.

Yellow card (aka "Scream") pubs tend to lop off about 20p from the price of every drink if you hold a Yellow Card.

Oddly, as the card itself only costs a quid, then you don't even need to remember to keep hold of your Yellow card as a new one will have repayed itself after 3 rounds.