Thanks for all the suggestions - very welcome and appreciated! I’m going to print out this list and try to figure out some things. To answer some questions:

I’ll probably get to London on Thursday morning and find my way to the hotel. I’m planning to have Friday to do whatever, then our group is meeting at the hotel Saturday afternoon/evening for a reception. Sunday morning, we’ll get on buses and go to numerous amusement parks, staying in different hotels as we travel around (hence the question about securing my passport). I think we’ll end at the first hotel. If that hotel has a safe (not an in-room safe), would it be wise to lock up my passport there? I believe we’re scheduled to go to 14 parks in 12 days, or something equally crazy. If you want the list, let me know.

I’m planning to only take one rolling suitcase plus my totebag. A friend suggested that I check with the hotel to see if I can store the suitcase there on arrival, before check-in, since I don’t want to drag it around.

I’m not much interested in Buckingham Palace, Tower of London, Harrod’s. etc. but will be happy to see them in passing. I like the idea of the tour buses that I can hop on & off.
Someone mentioned Stonehenge. Due to numerous requests, a stop at Stonehenge has been scheduled for the first day. I’ve been to Foamhenge (http://www.thefoamhenge.com/) and am looking forward to seeing the real thing.

I have a cell phone but it’s an old flip phone, nothing fancy. I’m considering getting an inexpensive fancier phone for the trip, especially if it can double as my Kindle, GPS, etc. Any recommendations for phone and/or apps? I don't want to overcomplicate this.

Thanks again!