The best part of being stuck in London for a week during the volcanic ash cloud situation last year was being able to eat at all my favorite places in the Kensington area. All places are within walking distance of our nearest tube stop, Gloucester Road on the Circle, District, and Piccadilly Lines (yellow, green, and blue lines.)
For Italian we hit Di Mario's which probably has the best cheese bread I've ever had. The Rigatoni alla Arrabiata is out of this world.
For Thai we went to The Churchill Arms which is just a tiny cramped room in the back of a traditional pub. The staff is curt and they will try to rush you through your meal but that's only because they have the best Thai food for the price in the entire country.
For Indian we went to Kahn's which was recommended to us by a local food critic. We had him on one of our flights from New York to London and for the entire flight we bugged him about where to go for this and that near our hotel right by the Gloucester Road tube stop. Kahn's was his one and only mention for Indian and I don't blame him. It's amazing.
For pizza we went to House of Coffee/Caffe Forum. I've yet to find a great pizza place in London but this one is one of the best, though still very unusual. They have a great lasagna as well.
For Asian we went franchise and visited Wagamama in Earl's Court. They're all over London, all over Europe, and are now even in select US cities. Doesn't matter, there's something there for everyone and I love their edamame and curry dishes.
The rest of the meals we had were self-made. The airlines gave us $100 a day for food so of course we usually went to the grocery store and bought enough food for the day. That would cost us less than $30 and we'd have the rest of the money to spend on fun stuff. I used some of that survival money on a new pair of pumas. Karma got the better of me and I lost one of them going through Customs in New York a couple of months later. Yeah, that's right, I lost a shoe going through Customs. It's obvious that God didn't want me to have those shoes.
If you're stuck in the next Icelandic volcanic ash cloud that happens to hover over London, these are some great activities to pass the time, once you get done with the obvious things that is.
Abbey road- grab three friends and a photographer and take the tube to St. Johns Wood station
Jack the Ripper walking tour- meets every night at the Tower Hill station at 7:30pm
High tea at the Orangery in Kensington Palace. Very posh. In Hyde Park
Soccer game- premiership games are a tough and expensive ticket, but the lower league teams are cheaper and much more personable. You can even chat with the players you're seated so close.
Wimbledon- if you're cheap you can get the discount evening session tickets that start at 5pm, but you may want to join the queue before 4pm because it gets very long.
Camden Town and Market- random things to buy and weird people to look at, as well as many good bars and live music venues. I've always had a fantastic time at The World's End and met many interesting people there.