The Analysis of Burned Human Remains
By Christopher W. Schmidt, Steven Symes
Edition: illustrated
Published by Academic Press, 2008
ISBN 0123725100, 9780123725103
279 pages
Google it for a few sample pages in the googlebook version. Page 90 has an ICP-MS summary of some remains compositions. It is mostly calcium and phosphorus with small amounts of some metals (from the coffin I guess). This is not a total composition as ICP-MS cannot detect light elements (like carbon) or halides (F, Cl, Br, I). Should not be much carbon left at all. It would have all been combusted and exhausted in the flue gas.
Edit: I read some more. They don't allow metal hardware on coffins, so I dunno where those signals come from...maybe accumulations in the bones and soft tissues. From the way it's phrased it sounds like anything that was not in the bones is completely vaporized which makes sense.