Unlike your tiny travel shampoo or your TSA-safe micro-tube of toothpaste , there's something low-key sexy about a rollerball perfume. More than just a carry-on essential (because no one is getting their full-sized bottle of Gucci Bloom through airport security), you can slip a skinny glass bottle into the side pocket of any purse for an instant refresh when you're standing at the crosswalk on a warm morning, or trying to shake off that stale airplane feeling before heading straight from hotel room to dinner.