I have mixed feelings about credit cards. I think if you use a credit card to earn points which can save you money in the future, then they may be a good item to use - if you can keep them under control. Pay off your credit cards each month. If you can't, don't use them. Many credit cards charge absurdly high interest rates and that $100 shirt you needed will cost double in the long run. Think about it. Would you walk into Macy's, pick out a shirt, go to the cashier and say, "you know what, I'd rather give you double the money for this item?" Of course you wouldn't. But ultimately, that is what you are doing when you put something on a credit card.
Back in my 20s, I carried no less than 4 credit cards on me at all times. I thought having more cards in my wallet made me look cool. Add that to my Starbucks Gold Card - you know, the one they give you when you spend a fortune on coffee - and my wallet was filled with plastic.
Cool shirt...charge it. Cool sunglasses...charge that too. Vacation to New York, why not? Put it on the card. Before long, I had racked up $15,000 in credit card debt, not counting my car loan for the BMW 325 I needed. Looking back, I wish I could have slapped myself for taking on so much debt. I only recently paid it all off.
If you don't have the cash in the bank to pay for something, DON'T BUY IT! It sounds like an obvious piece of advice, but trust me, it's easier said than done. Especially when it comes to new shiny things that would seem more manageable if paid for over time, like that new Rolex or a trip to Paris. If you want to carry plastic, carry a debit card. You will get the same feeling and satisfaction as swiping a credit card, but you'll be using your money instead of someone else's money. And if that some else is charging you more than 5% interest - which is extremely low in this environment - then you really don't need to spend the money to begin with.