I recall reading that when one is done with his lulav, he should save it and use it for another mitzvah (such burning chameitz) because once something has been used for a mitzvah it should be used for another (see this answer). Some of the subtleties are mentioned here. I'm still not sure if "any" mitzvah would count, but my current concern is limited to one practice.
But I also see that many people use their etrogim to make etrog jelly. Does that satisfy this same continuing of "honor" for the item used for a mitzvah? This site discusses the eating as a segulah for pregnant women but does that rise to the level of mitzvah? Would it mean no one else can eat it because for others, it doesn't hold the same sacred position? Is simple "eating" a mitzvah that would count?
