Aloe vera gel. Look for a brand without additional ingredients or you could even grow your own plants.
was thinking some more about this, and mango kept coming to mind.
it's sticky and turns gel-like in a pie, for instance. But it would seem to leave some unsightly orange particles in your tresses :)
Then I found this:
After just a glance, it appears to be vegan, though you'd have to do your own research and decide if it's a wise thing to apply to your hair.
I've heard about using flax seeds, grind them up, add water and heat, but you should look up the recipe to be sure. Makes sense since flax ground flax seeds are a binder.