Time it takes: 35 secondsSay no to a new store credit card. With rates typically above 20%, interest can wipe out that initial 10% discount. The new credit application will hurt your credit score, and you'll have yet another temptation to spend.
Check yes to reinvesting your dividends. If you'd put $10,000 in an S&P 500 index fund in 1997 and reinvested dividends all along, you'd have $22,446 at the end of 2006. If you didn't, you'd end with just $19,147.
Say no to an extended warranty. It'll cost you $30 to $200, and with electronics so reliable nowadays, you're unlikely to need it. Besides, if your computer breaks in two years, you'll want the new model, not a replacement.
Fill your tank with regular. Premium gas is about 8% more expensive, and no matter what the manufacturer says, cars don't need pricier gas to run smoothly and resist wear.
Swipe your debit rather than credit card. If your purchase will further fatten your balance on a high-rate credit card, you're better off paying with the money that's in your bank account. If asked, say "credit" rather than "debit" and your debit card will be processed over the credit-card network. You'll have more liability protection and less chance of paying a fee.
Delete any e-mail asking for account information or your social security number. It may be a scam. No reputable financial services firm will ask.