Yes, take extra batteries for your camera and a battery charger. We got a converter for the charger from Magellans last year that has a pop up switch on it to prevent overheating.

While it will be too late for this trip, you may want to consider a future trip from London to Paris (or reverse) on the Eurostar train. Lovely.

I second the London Walks recommendation. We've done both the local walks and the day excursions and the only one we wouldn't do again was the one to Greenwich. Very interesting and well done, but a lot of standing and listening. Not much walking at all. The boat ride to Greenwich and back was swell but you could take the boat on your own (in fact, you do on the return trip).

Very best wishes for a great trip,

Peggy