Odds are if someone steals your credit cards and goes on a buying spree it won't cost you anything. Federal law limits your liability to fifty bucks.
Most card companies will tell you that while it can cost you that $50, that fee is rarely applied.
Read all of the fine print when you get your card deal, because there are always exceptions. Card companies are more liable to ask for their money if you have done something reckless, like not reporting the card stolen for a year or more.