In the world of personal finance blogs, we spend most of our time trying to share ways to better invest or save money. It’s a worthwhile pursuit, and can make us so focused on saving every dollar, quarter, and penny that comes our way that we start to take wise saving – and wise spending – habits for granted.

And then there are those people who act as if money really grows on trees.

I’m always baffled when I hear these stories, whether I stumble across them on the news, another personal finance blog, or hear them directly from a friend. They’re always good for a laugh; hopefully, you’ll get a chuckle out of a few of these… that is, if you’re not guilty of them yourself.

1. Getting an oil change every 3,000 miles. Have you ever checked your vehicle’s owner’s manual? If you’re still following the advice of the folks at Jiffy Lube and changing your oil every 3,000 miles, I’m guessing the answer is no. Most vehicles only require an only change every 5,000 to 7,500 miles; some go as high as every 10,000 miles. Oil changes are a necessary expense, but at $25-$30 for each oil change, why double or even triple your costs by following the repair shop’s directives and not your vehicle manufacturer’s?

2. Buying brand name medications. Most name brand medications have a generic substitute; and most insurance plans reward you for making the switch. On our plan, a generic prescription costs as little as $5 a month, compared to $45 for a 30-day supply of the equivalent name brand pill. While it’s true that some name brand medications work better than the generic in some people, by and large, your health won’t suffer any negative consequences from asking your doctor to write you a prescription for the cheaper generic.

3. Not checking your receipts, invoices, bills, and statements. Every month, I review my transactions online. Why? Because my financial life does depend on it. Sometimes, companies make honest mistakes and accidentally bill you more; other times, they’re actively fleecing you, like AT&T has done to me countless times. Whether it’s a grocery store receipt or a bill at your vacation hotel, check it line by line as soon as possible, and report any errors immediately to a customer service representative.

4. Paying for things you’ll never use. A friend’s mother recently paid $110 to get a new passport book…which would be fine, except the woman has a fear of flying and hasn’t boarded a plane in 30 years. She could have saved herself $80 and purchased a passport card for $30 instead, which she could use when she drives to Mexico, or Canada, or takes a cruise to the Caribbean. But it’s not just passports; people pay huge amounts of money for huge data plans for their smartphones, then use next to nothing. My rule? If you don’t use it, then lose it.

5. Buying what you could get for free. One of the hottest gifts of the 2012 holiday season were tablet computers, like the Kindle Fire, the Barnes & Noble Nook, and Apple’s iPad. All these products let you download music, videos, books, magazines, and more, but at a cost. The thing is, most large, urban libraries contain all this and more, and it’s absolutely free. Sure, it may lack the convenience or novelty of an iPad, but why spend hundreds of dollars on a tablet, apps, and media materials you could get at the library for the price of a gallon of gas?

What crazy ways do you and those you know waste money?