*Wandering through Chinatown (near Leicester Square) looking at all the menus posted outside, trying to pick a restaurant for dinner.
*Browsing the food halls of Harrod's (Knightbridge). If grocery stores are the museums of food, then this is surely the Louvre.
*Shopping the street markets.
Enjoying the cuisines of the many different nationalities and cultures who have made London their adopted home.
Quick Tips:
*The street markets are a good source of food for a picnic lunch, or even a "picnic" dinner in the hotel.
*Ethnic restaurants often offer relatively inexpensive, good food.
*A full English breakfast is enormous -- eggs, sausage, bacon (closer to what Americans know of as ham), grilled tomato, grilled mushrooms, toast (cooled in a rack) -- if your hotel includes it, you may not need to eat lunch!
*For the most part, sandwiches leave a lot to be desired. Often they comprise two thin slices of bread, some butter, and a thin slice of meat. Things are getting better, for example, the Pret a Manger chain offers an interesting and more substantial selection.
Best Way To Get Around:
I'm a firm believer in public transportation, and London has a great subway and bus system. It has always gotten me where I wanted to go, even at night. However, if you're going to an unfamiliar area at night, you are well advised to take a taxi to avoid any worries about the neighborhood (or about getting lost). Taxis are plentiful, and the drivers have the reputation of being knowlegeable about every little street in London.