I guess I'm the lazy one here that doesn't really "track" anything. I just go in based off odometer. But I do keep the receipts somewhere if I ever need them.
But for me it's the major services 15K 25K 35K 45K that I've already paid for, and then I also do oil + filter changes and fluids topped off, and also a chance to notify if anything seems wrong on the 5K in between those. The extra oil changes are probably overkill, but I do plan to mod/upgrade to the S3 K04 APR kit when I pass the last 45K service, and I want everything to be in perfect working order when I do. So far I'm 2/3 of the way there and so far so good.
For fuel I check my MPG at the pump once in a while. And it's always been between 25-30 depending on how I drive. If it ever dips below without me driving hard, then I'll know I may need to get something checked out.