mobile - How do you handle aspect ratio differences with Unity 2D?

I've gotten a lot of answers to this question, but they are all generic and generally not very useful. None of the tutorials talk about aspect ratio and dealing with mobile devices and there are a zillion ways to do it, all seem to have gotcha's and flaws.

I really would love to know what successful games have used to handle different aspect ratios on iOS and Android without making a zillion different sized assets.

I am strictly speaking mobile, not desktop, specifically with Unity and I don't care about the UI, I only care about the gameplay canvas.

Issues I have in mind is when there are key things that have to be in certain places and cannot fall off the screen. Using black bars on top or bottom is unacceptable these days.