Protect photos and heirlooms. For irreplaceable old family photographs and other memorabilia, consider supplementing with digital backups stored online or somewhere offsite. Of course they can never truly replace the originals, but in case of fire or water damage, it can be reassuring to know you will still have some record of these bits and pieces of your family's history.
A good time to organize these items might be around the holidays, when relatives are visiting, so you can reminisce together. When it's time to put everything away, use acid-free photo or document boxes for photographs, drawings and other works on paper, and keep linens sealed in plastic or other mothproof containers.