Well besides the obvious physiological tier of Maslow's HoN, I would say it's a close tie between internet, television, and cell phone.
If I go somewhere without these things I really miss them. Example, I went to Switzerland for a week last month and my cell phone didn't work, we didn't have cable, and for the first few days we didn't have internet. It was OK but even in such a beautiful place I was really starting to miss these things.
90%+ of my waking hours I am utilizing one of these things, even at work (phone/internet). I'm even on my cell phone on the shitter. I guess cooking (~1 hr a day), playing guitar (~5 hours a week), and reading (~1 hr a day) are just about the only things I do where I don't need these things.