Money-Saving Tips in London

I figure I may as well do the same as for my Las Vegas trip and share the info for noobs travelling to London where everything is literally twice as expensive, so here are my ideas:

• Get an inexpensive cell phone for calls back home or for emergencies etc. It's a lot cheaper than you think. I picked up a Samsung phone for 4.50 GBP and 10 GBP worth of pre-paid airtime (which lasted me a week, your mileage may vary). This is simply impossible to get in Montreal.
• You can find internet cafes for as low as 1 GBP /hour even less expensive way to stay in touch with people.
• Tesco grocery stores allows you to buy some less expensive food and drink.
• Chinatown also offers a way to buy some good meals without breaking the bank.
• Use cash. From my experience, using credit cards means paying more fees than usual (on top of the exchange rate). I estimate you spend an extra 5% just because you use a credit card there.
• For the Wicked musical you can line up early at the official box office and buy reserved tickets for 25 GBP for front row seats (usually 60 GBP).
• Wake up early enough to eat an English breakfast for 4 GBP (for a jet-lagged, non-morning person like me this could be very tough accomplish)
• Shop around for the tour buses that best fit your needs. There are lots of options out there for your money.
  

That's pretty much all I can think of at this point. Just wear running shoes or something since there's a lot of walking to be done if you want to maximize your time in London.