I have a small woodworking business on etsy and ebay as a side hustle. I buy materials as I need them. This allows me to not have to wait 5 days for free shipping and not have to stock up and store as much stuff that I might not need in the near future. Plus there are no decent woodworking shops within 300 miles of where I live. I can have replacement material delivered to my door in 2 days...
I used to get most of the materials off of ebay, but every seller has different shipping preferences and costs. Amazon and their "2-day free shipping" has made my processes run a lot better. That being said, I really only care about the "2-day free shipping." The other stuff doesn't add value to my life. I would rather just have the option to pay a lower price for the "2 day free shipping" and pay more for other stuff if I wanted to get it later...
here are some examples of things that I typically buy as I am running out...