It's helpful to think of receipts as little dollar bills, because that is often what they represent.
Like when I picked up a prescription at CVS today. As the pharmacist handed me the receipt, she announced, "You have five extra bucks you can spend on any over-the-counter item in the store." Nice she mentioned that because now I'm likely to remember and not toss that receipt. In fact, I tossed the bag in my recycling stash already and just interrupted this paragraph to re-check my wallet to ensure I had not tossed what is, effectually, a five-dollar bill.
Money defined, is an object of exchange, and often receipts are just as good. Keep this in mind, my fellow savvy reader.
At this moment, I have four CVS receipts, with representative value of $5 (expires 8/19/2010), $3 (7/23), $1.98 (exp 7/23), $4 (exp 7/14), total $13.98 of real money tucked in there with my City of Chicago library card, Blue Cross Blue Shield insurance card, two grocery shopper cards and more.
Receipts ensure that when something breaks down or whatever, you are more likely to get it replaced at no additional cost or returned for actual cash.
A friend of mine spent $50 on a restaurant gift card for her boss. Months later, he told her that he lost it. But she hadn't kept her receipt, and both were out that fifty-dollar value. Bummer. So it's definitely worth keeping receipts even for a restaurant gift card that you would never expect to return. Just good to have on file, because your credit or debit card statement isn't enough for proof of a specific purchase.
I keep a simple file folder into which I drop all receipts that I don't expect ever to need. Those receipts I will need for tax or other purposes go into specific, organized folders. All the miscellany goes into this red one.
Taking a simple step might wield a bit of power for you, i.e., could be like real money in your wallet, sometimes. Worth the trouble, dear reader.
The only receipts I do not save are those for gas and those for restaurant meals I've already eaten. And these I toss only after making a note of them on the 3" x 5" index card I carry in my wallet. (A tally of credit card expenditures for the current period.) Or, if using a debit card, I toss the gas receipt after noting the line item in an old-school check register. That's just me.
Whatever your cash-flow style, get in the habit of keeping receipts around--even vaguely organized, somewhere at hand, because you'll find they sometimes come in handy as real money--i.e., an object of exchange that is of value to you.