LibraryThing has a discussion about weird objects used as bookmarks. For the most part these are discovered by librarians who deal with receiving and re-shelving borrowed books. I compiled a convenient list of such bookmarks. Just keep in mind that you will have to go through it in order to find out what the absolute strangest bookmarks are.
piece of bark
lock of hair
endorsed checks with a deposit slip
Abductees Anonymous member card
package of gum
outline for an unwritten book
chewed chewing gum
Even if you end up using one bookmark per book and leave in the book pretty much forever, a bookmark holder is a necessary, albeit somewhat overlooked accessory. This way you will always know where to look when you are beginning to read a new book.
Bookmark holders are typically made out of plastic, cardboard, leather or cloth. It is extremely easy to design one or even customized it. A great crafts project, too!
Book weights typically come under the name of weighted bookmarks. Personally, I never liked the idea of using anything but a flat paper or thin plastic bookmark, because other types of bookmarks can damage the book. The purpose of book weights is to hold down the book’s pages so they don’t close. Book weight is a great way to deal with a major inconvenience (especially if you are taking notes) without having to use bulky book holding devices. Leather is a common material for weighted bookmarks. I have seen some made out of wood or metal, but delicate book pages can be easily damaged by sharp edges of such bookmarks.