I think we can/should greatly reduce use of plastics by eliminating single-use plastic wherever possible. This mostly requires political will / habit changes. Although creating circular systems for e.g. food containers has its challenges, it's not moon shot difficult, we have these systems on small scales and we just need more people to use them.

I agree that fertilizer is a very difficult problem, it's possibly the hardest problem related to fossil fuels. Low-Tech Mag has covered this to some degree, and I'm in awe of the scale of the issue, as well as the dire effects of not figuring it out (people starving). https://solar.lowtechmagazine.com/2021/03/urban-fish-ponds-l... To some degree, I figure we'll just have to accept fertilizer as the last legitimate use of fossil fuels until we completely rebuild our farms / food production and sewage systems to be circular.