One of the most difficult decisions travelers renting a car face is whether to purchase the optional, but sometimes expensive, insurance from the company. "Many times, purchasing full rental insurance is unnecessary," says Cathy Lewis, MetLife Auto and Home's national rental coordinator. "A rental vehicle used on vacation qualifies as a 'non-owned' automobile under most personal auto policies, meaning that your vehicle's coverage carries over to any vehicle that you rent." If your auto policy doesn't provide coverage, a credit card might. It's worth checking. Other questions you should ask are whether you need collision-damage waivers and whether additional liability coverage is necessary and whether a personal auto policy provides complete coverage. In all cases, the best bet for consumers is to place a quick call to their insurance carrier or local agent before leaving on vacation. One other thing: While cars in the U.S. are usually covered, rental vehicles in foreign countries usually are not.