Having good credit will help you obtain car loans and home mortgages and even employment, since many employers now check credit reports as part of their employment decisions. Late payments or account charge-offs or bankruptcies stay on your credit report for 7 years or more, wrecking your chances of obtaining more credit down the line. You can apply for credit cards even with a blank credit reports, even without getting a loan co-signer. No other consumers can get cards this way, only college students. Credit cards are convenient when you don't have cash.
Credit cards are great for emergencies.
National credit cards help you build a credit report. Some local department store and gas cards may not. Banks now offer many customers enhanced ATM cards, called Visa Check or Mastermoney debit cards. They look and act a lot like credit cards. You can use them without a secret PIN code, either over the phone or at most merchants that accept credit cards.