In reply to The New NickB:
Oh dear, I might be falling foul of your rules on a few counts but let me justify myself.
I use a race number belt. Just a 5€ jobby from Decathlon. The number pins to it and I can spin it round front or back in a jiffy. On steep hill climbs, I like to spin it to the back so when I'm bent over, hands on quads, it's not getting in the way. Easy to spin back to the front.
Also on long ultras, as others have said it's best since you might be making several changes of clothes and being able to pop the race belt on and off is handy.
Now shorts - I just don't feel comfortable in the short ones where the mouse might pop out of the house if the lining has perished. I live in France and those kind of shorts are not very common but skin tight lycra is - I was commenting to a fellow runner the other day that basically I don't want to end up on a register. But then again this is a country that insists (as opposed to publicly frowns upon) Speedoes in public swimming pools.
There's also quite a high proportion of men with shaved legs in races here which I can't get my head round. Although the winner of the local vertical KM I did on Saturday beat me by 10 minutes (and he had shaved legs) so maybe there's something in that.