You don't have to necessarily dispose of items offered on your altar,...you could always create a new altar in your home or work place and recycle the items! or yes, donate it to someone who needs/wants the items or the center or use it as a decorative item! hehe. Like diamond girl, I know that once an item is offered to the Buddhas sincerely from the heart, it's already counted. Of course, you don't go having a bad motivaiton, thinking that whatever you offer can benefit you somehow..then that's opposite to what an offering should be.