This document is giving the most important information of CoAP, like options, codes, etc. in a compressed cheatsheet format.
(http://tools.ietf.org/html/rfc6690 "RFC6690")
(http://tools.ietf.org/html/draft-ietf-core-coap-18 "core-coap-18")
(http://tools.ietf.org/html/draft-ietf-core-block-12 "core-block-12")
(http://tools.ietf.org/html/draft-ietf-core-observe-08 "core-observe-08")