Actual answer: He crosses the river and takes all of the animals and the cabbage with him in one go. why not?

Alternative Answer: He just crosses the river. Why would he care who eats what?

Another Alternative Answer: He actually can't cross the river since he doesn't have a boat and neither the cabbage nor the animals serve as appropriate floatation aids

Yup, for your first one, no LLM has ever realized that I don't actually specify that he can only take one thing at a time. I think that's natural that it would assume that (as would most humans) because it would be so heavily primed to fill that in from every other version of the puzzle it's seen.

I will trust LLMs the day they suggest making a raft out of the lion's skin and propel it across the river by eating the cabbage and farting away. Goats are cool, keep the goat.