Definitively, my cell phone. It should be a smart phone. Because, wherever you go, you can keep in touch with everybody, in social networks, checking emails, surfing on internet, using customized gadgets, like maps, games, books, etc. Not only to be in touch, also you can use it like a memory extension: you can store important files, to remember important dates, address, identification numbers, to listen your favorite music and many other activities. I would go with a laptop. With it, you have all before mentioned but just one problem: the size. I prefer my cell phone.
One advantage more to add: you can make calls, too.