Use miles for upgrades on long flights

Unless you are a high-level frequent flier and get free upgrades, you have to use a hefty number of miles to get one. Still, it's always worth it on a long flight overseas. You get a better meal, more room to stretch out, and more and better entertainment options. New York to Hong Kong? No question. New York to London? Of course. New York to Chicago? Not unless you're a frequent flier and get the miles for free. One rule of thumb: 6 hours or more in the air—consider spending miles to upgrade.