We would run out of time. Of course we would. We can hardly finish a museum as rich as that before the official closing hour. For that matter we skipped a movie entirely and there were probably other buildings we missed. We did get to the gift shop. There we found some postcards we could send back to our hipster bar, and to our parents. And better, they had stamps good for international postcard mail. I could have bought any of the books there. (To be blunt, I could probably have written some of the ones about longitude and its history.) But I ended up getting a T-shirt, proclaiming the Prime Meridian, and I'd wear that the first time we got back to our hipster bar. I figure it to do the kind of duty that T-shirts from obscure amusement parks will do.
We walked back through crowds of Londoners scattered on the grass, and didn't end up going back the way we came. We went for the nearer subway stop instead. This would take us naturally toward the Cutty Sark, too. That was closed --- it shut the same time Greenwich did --- but we could at least see it and walk around outside.
This also let us discover Harry's Original Sweetshop, the better to pursue our quest for oddball candies. They didn't have anything remarkably strange there, but we were able to pick up a couple of things, with the thought of snacks on the next day's flights. They did have a nice-looking carousel-themed tin of candies but that seemed too big and too marginal to get for the plane. Too bad.
We went back home, to our hotel, and filled out postcards. And stopped at a convenience store opposite the Underground station in order to buy Starbars. We hadn't gotten them yet that trip, and we didn't get enough. (As it would happen, we'd end up with more than £15 in bills and change left over when we exited the country. That's not too bad in terms of guessing how much spending money we would need, but the amount of it does offend 
bunny_hugger who sees it as money we can't spend. And we could have got a dozen more Starbars with that, easily.)
We would have to mail the cards, certainly, but we knew where there was a postbox. That would be not far from the underground station for bunny_hugger's uncle, whom we could visit one last time. We did call him to say we were coming --- I think this was the time the front desk clerk insisted we couldn't have the number right because we didn't have the area code, when bunny_hugger had specifically looked up that the area code was not required --- but had to work to convince him not to pick us up.
This was because we wanted to stop in at the Waitrose supermarket also by the Underground station. He had casually mentioned one night how bunny_hugger had been drinking the expensive coffee and then we were wracked with guilt for taking so much from him. He wasn't upset, mind you, and I know he didn't begrudge us that, but we felt like we should get some coffee at least, to thank him and to replenish his stocks.
It happens we couldn't remember what kind of coffee he drank. I was close in remembering the cans he had, although we picked up an espresso rather than a regular blend. It transpired he just reuses the can, and had been drinking some wholly different brand of coffee anyway. Well, the sentiment was there, and understood.
We'd spend the rest of the night there, of course, again in that mixture of casual talk and stabbing confessional and tech support. This was when we finally got his new telephone connected, something that required moving a bookshelf, so good thing I was there. It's also when we got his e-mail passwords finally all reset, for which I was not needed at all. bunny_hugger's uncle spoke of himself as being at that stage where he has intellectually accepted some of the things he needs to do, such as to clear out their home of the things he no longer needs, but emotional acceptance still fails at the moment of doing. His mention of thinking how it would feel to have her coat wrapped around a stranger hit me hard.
It was a strange evening, a basically happy experience glazed with the fear that we might never see him again, or even might never see him in this place again. (bunny_hugger's mother insists he ought to sell the house and move back to the United States. He spoke some of maybe doing that, only he wouldn't want to move back to Michigan, where his family is. The East Coast, maybe. If we could buy him the house just south of ours that might be almost perfect.)
He did say that we'd restored his feeling of living. What a responsibility to have.
Trivia: After 1916 the British government took over the importation of tea for the duration of the war, and imposed price controls on 90 percent of sales. The tea was divided into four (in 1918, three) grades for sale. Source: Tea: Addiction, Exploitation, and Empire, Roy Moxham.
Currently Reading: Love Conquers All, Robert Benchley.