I'm Antipodean and grew up on metric but can do all the imperial measurements. Both the US and UK like to not use metric (or some hybrid).
Kilograms are pretty easy. 1 L of water is 1 kg. 1 pound is 0.4536 kg but it's usually easiest to just use 0.5kg for a rough estimate and that makes it 2 pound to 1 kg. If more precision is needed then a calculator is never far away.
For temperature:
-20° is dead (it's not really, but Australians tend to feel this way), I believe this temperature can be dangerous without adequate protection
-10° is Australia also doesn't really get this temperature
0° is jacket temperature, and freezing water, although the freezer is usually at -3-5° (I think)
2-3° is the fridge temperature
10° is jumper temperature
20° is roughly t-shirt temperature
22-23° is a nice comfortable temperature
25° start of a heatwave in the UK and NZ, still cool for Australia.
30° is not nice temperature unless you have a pool or aircon handy.
40° is "what are you doing moving around" temperature. Find aircon or swimming pool urgently.
45-47° is "you shouldn't have gone out to the desert" temperature.
Like imperial to metric this definitely also comes out with currency conversion. Having travelled a lot, the first few weeks are definitely the hardest, then it starts to become intuitive.
The GBP to AUD is fairly easy because it's roughly 2 AUD to 1 GBP. Things like Norway/Sweden/Denmark are harder because it's 6.90, 7.50, 4.50, these tend to just be rounded to 5 and 10, which is generally close enough to not make stupid mistakes. Things like Hungarian Forint are a bit harder again 1.00 Australian Dollar = 231.49064 Hungarian Forints, But again it's just rounding to 200 and then establishing thresholds. 10 is 2000, 50 is 10000, 100 is 20000, 1000 is 200000.
Kilograms are pretty easy. 1 L of water is 1 kg. 1 pound is 0.4536 kg but it's usually easiest to just use 0.5kg for a rough estimate and that makes it 2 pound to 1 kg. If more precision is needed then a calculator is never far away.
For temperature:
-20° is dead (it's not really, but Australians tend to feel this way), I believe this temperature can be dangerous without adequate protection -10° is Australia also doesn't really get this temperature 0° is jacket temperature, and freezing water, although the freezer is usually at -3-5° (I think) 2-3° is the fridge temperature 10° is jumper temperature 20° is roughly t-shirt temperature 22-23° is a nice comfortable temperature 25° start of a heatwave in the UK and NZ, still cool for Australia. 30° is not nice temperature unless you have a pool or aircon handy. 40° is "what are you doing moving around" temperature. Find aircon or swimming pool urgently. 45-47° is "you shouldn't have gone out to the desert" temperature.
Like imperial to metric this definitely also comes out with currency conversion. Having travelled a lot, the first few weeks are definitely the hardest, then it starts to become intuitive.
The GBP to AUD is fairly easy because it's roughly 2 AUD to 1 GBP. Things like Norway/Sweden/Denmark are harder because it's 6.90, 7.50, 4.50, these tend to just be rounded to 5 and 10, which is generally close enough to not make stupid mistakes. Things like Hungarian Forint are a bit harder again 1.00 Australian Dollar = 231.49064 Hungarian Forints, But again it's just rounding to 200 and then establishing thresholds. 10 is 2000, 50 is 10000, 100 is 20000, 1000 is 200000.
And I went down a rabbithole :)