[Error: unknown template qotd]Easy: phone. I got along fine without one for years longer than everyone else did, and I use it maybe a couple of times a week to call my family. Oh, and I also keep my calendar in there, but I used to keep a hardcopy one on me and could easily do that again for a week.
(For the record, TV would be the second one to go. Again: easy.)
(For the record, TV would be the second one to go. Again: easy.)