The purpose of school is to equip students on how to teach themselves, not to spoon feed them facts. For that reason, philosophy, rhetoric, logic, music, literature, and mathematics should be the priorities. Students who are well-versed in those areas WILL figure out the rest of it a million times faster than some kid who drilled on history, science, or other facts. Teach the kids how to study history, don't feed the…
'Science' is also a method - one that took a long time to develop - and is fundamental in understanding the universe. It should also be included in your list of essentials...
How great would it be for a kid to ask "why does rain slide off of leaves?" rather than be told all the different leaf shapes and tree types? How excellent would it be to have a kid spend time documenting all the different types of clouds and offer a hypothesis on their purposes rather than just telling them the formal names and descriptions? Teach them the process, don't make them memorize. No one ever said, "wow, I really am glad they taught me the difference between cumulus and cirrus clouds in middle school science."