I've been thinking about this since I first saw this question, and couldn't come up with an immediate answer - the reality is that it's everything I have, or nothing that I have. But in terms of those things that I use daily and enrich my life, I would say my car. Sure, I could get by with an old beater that gets me from point A to point B. But I really enjoy my BMW 535 i xDrive and look forward to driving it every day.
And, as Sunnylea mentioned, my Kindle App on my iPad.