Skip the Hotel, Get a Rental
Hotels in London can be rather pricey, especially considering that even the costlier ones can be small and cramped. To keep a few quid in your pocket, opt for a rental service like Airbnb and get a room or a flat in a part of town you'd like to explore. At a hotel you pay for the convenience of being near major attractions, which tends to keep you in more expensive touristy areas. By using a rental service you can find a neighborhood location that offers cheaper eats, less crowded transportation hubs and a sense of how real Londoners live.
Hop on the Tube with a Visitor Oyster Card
The new Visitor Oyster Card offers a cheaper alternative to buying a Day Travelcard. By capping how much you spend each day at £6.60, you spend roughly half of what you would on a Day Travelcard (£12.30.) You can apply online and have it shipped to your house before your trip, ready to use as soon as you step off the plane! Make sure to order your card in advance to get the lowest prices!!
Sandwich, Sandwich, Sandwich
Okay, this is going to sound lame, but I'm in love with the simple little British sandwich shops that are pretty much ubiquitous in the capital. Whether it's a M&S or Pret a Manger, little sandwich shops offer a quick pick me up and a pretty cheap food option in an expensive city. Instead of eating in, grab your sandwich to go and sit in front of a museum or attraction for prime people watching. By avoiding the cafes at tourist attractions, you can save a lot of cash.