Depending on the ages of any kids you've got with you I'd try for some on the day tickets to the Woman in Black at the Fortune Theatre on Russell St in Covent Garden. Disregard the film totally, it's worth seeing.
Covent Garden is lively, you have the market there and plenty of pubs. I'd also make use of the riverboat if you can. Greenwich and the O2 are some of the furthest east stops and then it can take you all the way into central town or further west without the sweaty congestion of the tube. It's dearer than the tube mind.
Goddards pie and mash in Greenwich is a good pie and mash, but if you're anywhere near Tower Bridge I'd try Manze's on Tower Bridge Rd or Cooke's in Broadway Market if you're near there.
There's a lot of outdoor cinemas on rooftops and in parks that aren't bad value,especially as you can take your own grub and booze to a lot of them.