I suspect most people here don't work with other people (just the impression I get lol #asknostr )
I tend not to go to work Xmas parties, I find they can be depressing, there's always a sally from operations crying about nothing and a Henry from sales is shouting at ghosts.
I try to avoid secret Santa, mostly cos it's really awkward, and don't know the person, nor they, me.
I donsugn the leaving card, but just make a variation of something someone has said before me, or combine a few of the previous ones. (You can never go first). I usually have no idea who it is anyway.
I like your approach tho! You've nailed office life!!