How to make your own oxygen absorbers. https://healthrangerreport.com/prep-with-mike-how-to-make-your-own-oxygen-absorbers
8 minute audio. Yes Mike is selling stuff, but the information is good.
Short version is 00 steel wool, salt, and something to to put it in to keep the rust from transferring to what you are storing. I used an old sock. The salt causes the steel wool to rust easier and attracts moisture which uses up the 02 and water vapor to make rust. The reaction also can make a little heat. I've heard that it is similar to what they use in hand warmers.