I think in terms of fahrenheit for hot temperatures and celsius for low ones. For some strange reason.
In Britain an entire generation (or more) of us grew up with kilometres, metres, and centimetres, grams, Centigrade etc in the Science labs at school, and with feet and inches, stones, pounds and ounces, Fahrenheit, etc etc, in the real world we actually lived in. I can still cope with that fine, and can use either Imperial or metric in, for example, cooking. (Though growing up in my mother's kitchen, it was all cups and tablespoons, far more convenient, and I still use these measures when baking bread. It was further complicated by the fact that my father was Canadian, so several of our cookbooks used Canadian measures.)
But when I'm in France I happily think in kilometres, not miles.
What I do find interesting is the old money, although I do find it hard to get to grips with it, with all the farthings and tuppence and stuff. But like I said, I find it interesting. Am I right in saying there were 12...pennies in a shilling? I always get it wrong!
Farthings had just gone out when I was at junior school, but our ancient textbooks still had them, so I had to learn them. Tuppence just meant two pence, and we have a two-pence piece now, though we didn't then; what we did
have was the wonderful 12-sided threepenny bit. And though we never used them, I also had to know about rods, poles & perches (all the same thing), chains, furlongs, etc etc. The back cover of school exercise books always had all of these listed, and many more. Sadly long gone -- so if I want a nostalgic "fix" of old weights and measures, I have a couple of brilliant conversion programs on my computer: Quad-Lock Unit Converter and ESB Unit Conv -- and they have ones I've never even heard of.
And what is
the point of a metric tonne, when it's 0.9842 of a good old-fashioned proper ton?