I'm gonna traval to another country for 3 months, left my A4 at home without driving.
Do you have any good tips to keep the car as "healthy" as possible, given that it won't be driven for such a long time?
Thanks so much!

Indoors - no problem, outside - car cover tied on. There are some issues with mice building nests. Had that problem when I lived in Connecticut. California is no problem, so it depends a bit on where you are.

I have a friend with an RS6. He stores it indoors with a cover andwith the alarm on for 6 months at a time and it starts right up with no problems.

You may have a problem with any gas left in your tank oxidating. So the best way to prevent this is to pick up some fuel stabilizer at auto zone or something and put it in your tank before you leave. Also, fill your tank up all the way before you leave.