I have a caravan key on my "minimal" keys - 1 car key, one caravan key, one front door key for home. Oh, and a spare key for Mrs Gozza's mobility scooter.
On a second key ring I have the two keys to get into the storage site, keys for each of the caravan immobiliser locks, and the cut off key for the motor mover. That key ring has a second habitation key for the caravan.
So yes, whenever we're away in the caravan we have a spare key with us.
Spare car keys we're not so good with, but I try to be strict with myself about always having a spare car key with me, whenever I'm far enough from home that getting back to collect a key would be a nuisance - a lesson I learned one day when I dropped the keys in a puddle and killed the bit that turns off the immobiliser. Luckily I was only at the storage site and I'd already dropped Mrs Gozza at home, so she could come in the other car with my spare key, but she wasn't pleased!