One thing that the Classical Education and Cultural Literacy movements have been very good about is bringing up the importance of familiarity with the standard pagan mythologies of Western culture. There are some great books out there for kids of Greek, Roman and Norse mythology. However I wonder if (outside of religious circles where it is taught as part of catechesis) the standard Bible stories, which are equally a part of Western Culture and referenced even more often than pagan mythology get as much play.
There's a group out there called the Bible Literacy Project which has apparently put together a public-school-approved high school book on the bible as cultural literacy which is now in use in various school districts in 30 states. There are some sample pages from it here. (Skimming through, it looks moderately good at first glance, though I think I'd put it at 6th or 7th grade rather than high school.) There's also a Time Magazine article about the program here.
It seems like an interesting approach, and I think the point is well made that in order to understand much of Western art and literature you need to know the biblical stories to which people were referring. There is, of course, also a danger of demythologizing scripture and treating it as nothing more than a large book of primitive literature. Still, given the current state of cultural illiteracy among many of today's public school students (Christian as well as non) I suspect that being exposed to all of this in a systematic fashion is much better than not. And getting a guided tour through where all of the books came from and what messages people have drawn from them is probably much more useful than a kid without any religious formation just pulling down a bible and starting to randomly read around without any direction.