The birthday present was a kayak drogue - sea anchor, sea sock, drift anchor, parachute brake are also among many terms used for this bit of kit, but I'm sticking with 'drogue', as it's the shortest. I'm familiar with drogues being used on yachts and motor boats in heavy weather at sea, but I'd never come across a kayak drogue and, for the sort of quiet paddling I do, I did wonder whether I would ever use it. So I did a bit of research and discovered that drogues are used quite regularly by sea anglers fishing from sit-on-top kayaks - mainly to slow down their drift across fishing grounds when it gets a bit windy. This was a bit of an eye opener and, although I'm not an angler, I could now visualize occasions when I might want to use a drogue in open water.
Update (several days later): I've only just noticed that the loop of webbing at the smaller end isn't actually showing in the photograph! It is there, as seen in the next one.