It’s obviously my "smartphone"!
Mainly because my entire profession revolves around it. My work won't be as efficient as now without it. It totally revolutionized the way we interact with people not only in our professional life but also in our social life. I won’t last a day without checking my social media status, it’s really important for me.
I think that if I remove my smartphone in my life, I will survive, but it wouldn't be as productive when I have it. Basically everything that I need in my everyday work is carefully stored through different apps in my phone.
The good thing about it is that it keeps evolving. I wouldn't be surprised if our smartphone will become a "personal" companion in the future.