I think the whole purpose of the ritual is shared solemnity. Laying aside Matthew 5:34-37, using the Bible fits in the context of Western civilization. Likewise, using nothing and merely affirming fits as well. But by its very nature bringing in any book or other item because it has "meaning" to you doesn't fit. It violates shared solemnity by the individualist nature of the act and opens the ritual to trivialization. What's next, someone's Teddy Bear?