self-determination (maybe this falls under your excluded values, character traits, or philosophies), but its a rather important skill in my opinion.
a second language - doesn't matter which one really, but it has clear cognitive and practical benefits. Bonus points for spending time in another culture for a different perspective.
edited to add: Really many of these skills can be learned as needed, but the desire and skills to learn new things are an important skill to have. If you're successful in teaching them the fundamental ones, like critical thinking, then they have the tools to learn what's needed.
a second language - doesn't matter which one really, but it has clear cognitive and practical benefits. Bonus points for spending time in another culture for a different perspective.
edited to add: Really many of these skills can be learned as needed, but the desire and skills to learn new things are an important skill to have. If you're successful in teaching them the fundamental ones, like critical thinking, then they have the tools to learn what's needed.