A note from the Kumamoto International religion desk (merged with other various desks for obvious reasons): Some shinto religious omamori (お守り、amulet) manage to retain their protective powers over an entire year, at which time they must be replaced by others which are identical in appearance but renewed, while some peter out protectively in a few weeks. But in neither case may you casually huck them out with the garbage.
Omamori of the former type are generally disposed of at a shrine around New Years (where, conveniently, new are available for purchase), but the New Years decorations (shimenawa, しめ縄, are most common) miss this boat. Consequently, an event to dispose of these is held in most neighborhoods, usually on the second Saturday of January, called “dondoya” - kind of an interesting word. It is a portmanteau of「尊や尊」(tou ya tou - respect and respect)、the phrase for “speedily” (どんどんと - referring to the rapid burning), and an onomatopoeia of the sound the bamboo traditionally used as the combustible material makes as the gas in each of its separate chambers expands and explodes. Participants often roast mochi over the embers, though I usually brought enough marshmellows for all the neighborhood kids (I was a popular dad).
Check around your neighborhood for the location and date it will be held. It’s actually quite fun - and convenient for relieving oneself of amulets. - William