We didn't study the Opium Wars in history at all throughout my education, I learned about those on my own thanks to the Internet. The entire Middle East, our influence in South America, etc, none of that was covered in school, and I went to some pretty good public schools. (E.g. in High School we edited DNA of Bacteria)
For that matter, I think China was only mentioned in passing throughout my entire education. WW1 was also only mentioned very briefly (maybe a couple weeks? Archduke is shot, shit goes down) and then we spent a fair bit of time on WW2, but less than we spent on Ancient Egypt honestly. (I think we spent an entire 2 or 3 months on Ancient Egypt).
We spent a fair amount of time on the Reformation and Renaissance, ancient Greece and Rome, and US history was mostly a ~bullshit~ censored history of the founding of the US. The Washington State history classes went into some history of the local tribes, but failed to mention any of the fun details about how Seattle was founded (prostitution, drinking, Seattle literally poisoning the wells of nearby towns to force them to join Seattle to get access to clean water)
College was better, mostly US history and World History, still nothing about the far east though.
We did an excellent segment on the US Revolution in College, including the funding source behind the revolutionary war, that was very interesting.
Edit: Sex ed was pretty comprehensive, and we ended the quarter by watching Rocky Horror Picture Show, so that was fun. (The Nerd and Goth kids formed a voting block for what movie to watch. :D) I am still surprised they talked about so much about forms of contraceptives that almost no one uses (spermicidal gels and foams), but at least they properly demonstrated how to use a condom, so that was good.
For "don't smoke" the health teacher had lots of pictures of tumors.
Alcohol wasn't really talked about, but honestly in the 90s we didn't know a much about how unhealthy it is as we do now. (Doctors knew it was bad, but just in the last few years research has come out showing that the safe amount of drinking is none)