Everyone knows that it's most responsible to pay cash for items rather than charge them, but there are some things that you should always pay for with plastic. Apartment Therapy lays out what you should buy on credit rather than with cash.
Most credit cards will give extra protection or an extended warranty on electronics. So buy your electronics on credit and save money on an extended warranty, plus be protected if the electronic breaks or is damaged.
Travel expenses, especially out of the country, should always be paid for with credit card. Of course, you'll need a little local currency for those merchants where you can't use plastic, but by using your credit card to pay for most things, you'll get a better exchange rate. You also can easily get a replacement credit card if your wallet is stolen, but cash is irreplaceable.
Credit card companies will often provide insurance on rental cars for free, so find out for sure and use your credit card for any rental cars if yours covers insurance.
Use your credit card to pay your bills every month for convenience. Put all your bills on auto-pay and never worry about late fees or stamps again! One caveat, if you have to cancel your credit card, keep a list of bills you have set up to be paid with it so you can change your information quickly.
Paying by credit card for any reimbursable expenses gives you a second accounting, above and beyond receipts, of what you purchased so your company can reimburse you.