I have a single house key on a ring that snaps into a specific [small] purse. I rarely use that purse, but I use this key ring the absolute most since I walk a lot of places from home.
We have two cars, but not his and hers. Whoever is driving the farthest that day drives the most economical car.
One car has a fob, but not an actual key (keyless entry and electric start). Since I need a license with me to drive, but not to walk (LOL), the fob just lives in my [small] purse and I toss in (or snap in) the single key when driving this car.
The other car has a key and a fob, so I have a different key ring with those two items and (a second) house key and our mailbox key on it.
I have a single ring for my dad's house key. He lives a minute away on foot.
I have a single ring with our pool & tennis courts key and (a third) house key. The tennis courts are close. The pool is farther away than grandpa. ;)
All those rings hang on a three-hook pub mirror by our front door, which is not visible from any window or door from the outside.
DH has one key ring with (a fourth) house key, car key, car fob (car with fob and key), mailbox key, and two work keys on it. The car with just the fob doesn't go on a ring very well, so that gets shoved in his pocket.
All the house keys came with the new locks when we purchased the house, so we made use of them. ;)