We needed some thank-you gifts and such for people, so our solution to this was to go to Borough Market. Borough Market is a covered food market on the south bank of the Thames, near Tower Bridge. It's a bunch of stalls selling a wide variety of produce, meat, seafood, and most importantly, cheese. We got some cheese, tea, and balsamic vinegar to give as presents, and also availed ourselves of the market's food stall area (like food trucks, but semi-permanent and under tents). It's a good place to get a reasonably cost-effective lunch. We also went back to Greenwich Market and bought a painting of a cat stylized to look like Picasso had done it.
We had time for one more museum after this, and it wound up being the Victoria and Albert museum. It's the largest decorative arts and design museum in the world, so it has examples of decorative sculpture, pottery, architecture, objects, and the like from every corner of the planet. There's carpets from Iran, porcelain from China, bits of churches, curiosities from India (like the most metal wizard's hat ever, adorned with lethal circular throwing blades, and a statue of a tiger mauling a soldier in red and blue that makes noises like a dying man when a crank is turned). It's too big to see everything, we got there about 3 hours before it closed, and Adam was starting to run out of steam, having spent most of the past couple days powering through a cold, so we missed a fair amount of this museum. Next time, perhaps. We had dinner in Soho at a ramen restaurant (and found a place selling jamon iberico, and had a snack on that), and then went back to our hostel to sleep before the next day's journey through aviation hell.