Depending how "technical" one wanted to get, every pre-d20
TLG item could be considered related to C&C, but only on the thematic line, in that C&C was derived, in part, from the earlier 'sword and sorcery' game system. This would then include things like the After Winter Dark folio, The Fantastic Adventure, etc. When
d20 was released, these got "updated" and then 'updated' again for C&C (at least some of it.) And then, depending again on how technical one wanted to be, anything within the Erde/Aihrde world, which would include all modules directly written by a Chenault or Mac Golden could be included, since that setting is the assumed default, without being officially written into the 'core rules' as such.
Really, I would probably not go that far.
Those who can, don't. Those who should not, do.