We have an emergency game kit in the trunk of our car. Basically, it's for those situations where we find ourselves in a place without anything much to do, and we don't want to mess around on our various electronic devices. Its contents vary depending on our whims, but we've often kept Zombie Dice in there, Cthulhu Dice, a print-out of an "escape room" from Escape This Podcast, and – in the past couple of years – a grocery-store find of lateral-thinking-type puzzles (filled with "there's a cabin in the woods full of dead people, with no footprints around it" types of riddles). We rotate out games or elements as our whims and collection inspires us, but our criteria is small, portable, quick, and replaceable enough that if we forget an element at an I-65 fast-food joint, it won't be too challenging or expensive to replace.
If you have your own emergency game kit, feel free to swing by the forums and share what you find indispensable; we're always looking for ideas! If this post inspires your own EGK, it'd be fun to hear about that as well.
-- Steven Marsh