[Lostbrain]

I'd say look for the things to do that don't cost anything. Hanging out at Southbank is my favorite, in front of the Barbican there is always something going on. Most of the museums are free as well as the National Gallery and National Portrait Gallery. Some of the markets are great - Colombia Road on a Sunday is a huge flower market, Kensington is a crazy eclectic mix and Spitalfields has some great clothes.

You can try to keep food costs down a bit with offers on various chain restaurants - Pizza Express always has deals if you sign up for their emails. Lots of interesting and not too expensive street food too - head to Borough Market at lunchtime - it's amazing.