Answer:
It all depends on what you want to call a drum kit. So I guess it's anything with at least 2 percussion instruments of which at least 1 is a drum.
Some drum kits (if we're talking about non live players) have big drum kits on their harddrives. I personally like each of my kits to contain
10 kicks
10 snares
10 hi hats
10 open hi hats
Etc...