What's taking up space in *your* pack?

[uninspired]

I'm in the midst of packing right now, thinking about how much I'll miss my flatiron and my laptop and all those other nonessentials I can't justify carrying around for three months. And then I look at my stack of disposable contacts, my bottles of contact solution, my glasses and the two somewhat weighty paperbacks I'll lug around. Both the contact stuff and the books are space-eating and heavy-ish, but if I left everything else behind, I'd still take them.

So, I got to wondering--what're the things you absolutely couldn't leave behind, either because you "need" them, or you need them?