You don’t want to get stuck with fees for checking two bags on long trips, so you should own one mondo-size trunk on wheels. If you need to bring helmets and other gear, consider going as large as 9,000 cubic inches; most people will be happy in the 5,000-to-7,000 range.
WHY THIS ONE: At 5,310 cubic inches, the Thule Crossover 87L Rolling Duffel has a narrow profile that moved nimbly through crowds, solid oversize wheels that didn’t blink at tall curbs, and a rain-shedding exterior. Best of all: nifty crushproof pockets for goggles and an iPod.