Frequenting the pubs is a key survival tip, it's the only place where you have any chance of getting something edible for a reasonable price.
Sorry, I have to disagree here. There are loads of great places to eat in London, here's some examples off the top of my head:
Woodlands, Marylebone High Street (Great, central, cheap South Indian food)
Rasa Sayang, Chinatown (Cheap but good Malaysian)
Tayyabs, East end (Great but cheap Pakistani food, behind the mosque, big queues most of the time)
Royal China, all over town (Pricey but good Chinese, good for dim sum, big queues weekends)
Meson Don Felipe, The Cut (yes, that's the name of a street) (Spanish Tapas, cheap, good wine, good atmosphere)
Hafez, Hereford Road (Great Iranian food)
Tas, all over town (Acceptable Turkish food)
Gordons Wine Bar - wine bar dive in the middle of town for a change from pubs, of which there are few good ones in the center
Princess Garden, Mayfair (Moderately priced dim sum)
Mildred's, Soho (Moderately priced veggie)
Avoid Convent Garden, Leicester Square, Brick Lane, and other touristy spots for eating/drinking (though Chinatown/soho is OK) and you should do fine. Most pubs will serve rubbish food in my experience, though there are some gastro pubs which do quite good food - if it's a trendy pub it might do quality food, otherwise probably not. Don't rely on reviews on google maps, which are often completely off base, ask a local.
As for geeky things, don't forget the observatory in Greenwich, on the top of the hill in a lovely park with great views of London, plus the foot-passage under the river Thames which leads from Greenwich to the Isle of Dogs - worth a day trip on the DLR if you have the time.