If a charity sends you unsolicited materials, you are free to keep the materials or dispose of them and are under no obligation to send the charity money. Basically, charities often mail out such goodies as an enticement to the recipients to respond with donations, but the charities do this knowing that the percentage of people who will actually donate is quite small.
With religious sacramentals, an object that is blessed should not be thrown away but either burned (if burnable) or broken up and the ashes or fragments buried. Charities should tell you in the promotional literature if the object has been blessed. If there is no mention, then you are free to assume that the object has not been blessed. However, if you feel uncomfortable disposing of unblessed sacramentals, you can collect the stuff you receive in a box and donate the items – including any blessed materials you can’t keep – to a local Catholic hospital, prison apostolate, parish or diocesan ministry, or other such Catholic group that would appreciate having such materials to distribute to the needy.