Forget crying over spilled milk; it's melted makeup that makes me weep. If you live in a warm climate or plan to travel to hot destinations this summer, keeping your makeup cool is a major concern.
As someone who's been known to sneak my makeup to the beach, I'm loving this IcyBag Cosmetic Bag ($14.99). The roomy pink-and-tan pouch comes with an ice pack in the bottom (like a lunch tote). Just store the cool pack in the freezer and slip it into the insulated bag before you leave; it's waterproof, so it won't soak your stuff even as it warms up.
Thanks to Elke Von Freudenberg's blog for the tip.