So for ether you need ethanol and acid. Acid is easy to make with salt water, so find a swamp and post up to make acid water, then boil that for concentrated acid. Easy peasy.
Ethanol is a bitch and a half on the other hand. You’re going to need a brewing book for sure since ether is a distillation of alcohol. Unfortunately you will also need a thermometer which is strangely difficult to find and also impossible to craft. And whatever alcohol you can find/craft en masse since most can be distilled into ethanol the only thing that matters is what is the easiest for you to get. Oftentimes this will be moonshine (buckwheat or cornmeal), fruit wine (just gallons and gallons of fruit juice, however you can get it.), or vodka (sugar straight up)
Easiest of these imo is vodka. You can make sugar with sticks and acid at cooking level 7, which you should already have if you’re going to be attempt to bootstrap anasthesia kits, so once again, post up in a swamp, make acid, fell trees, ruin the world.
For the medicine itself poppy painkiller is the easiest to craft, and unfortunately the only way to do that is to walk around fields gathering poppies by hand.