Idaho Centennial memorabilia bought this year may be worth more than its purchase price - someday.

Some items could increase in value within five years, and therefore have value. Others may take 25 to 50 years."The rule of thumb is it takes 50 years for a run-of-the-mill item to become collectible," said Danielle Warnes, a collector for more than 30 years who writes about the subject for the Chicago Sun Times. "Don't buy it unless you really like it because you may sit on it. That should be the caveat for all collectors."

The more unusual the item, the more likely it will be valuable later. Warnes said disposable items, like foil-covered chocolate coins or candy bars, are among some of the mostly highly collectible items because they quickly become scarce as people eat them.

Thimble collectors already have purchased several thousand Centennial thimbles, said Dave Hunt, owner of Treasure Valley Gifts.