Being a tourist hotspot there are food outlets everywhere. Probably the cheapest is Macdonalds. and Weathersppon Pubs offer a decent menu at reasonable prices.
Recommend China town for a decent chinese and Whitechapel for indian restaurants.
Restaurants! Try Borough Market
There is a very comprehensive restaurant guide at www.timeout.com/london
There are thousands of restaurants in London.
Which bit are you going to, what's your budget, and what are your cuisine preferences?
You have to start by asking what country's food you want, then that narrows down the list of restaurants a bit.
im going to london for my 18th with my 2 friends, anyone know any good places for breakfast, brunch and a late evening meal?