I'd like to add my 2 cents to this topic, because it's something I am concerned with as well. I reuse clean packing materials, and I ask some trusted people give me what they collect as well. If you live near an Ikea, the dishes in their kitchen department all have thin foam pieces in between. People leave those on the shelf when they buy dishes, and the employees just throw them out. They will give them to you if you ask nicely. There are probably all kinds of businesses like that where you can ask for supplies. Reusing something is better than buying new, if it was already heading for the trash. I like the idea of the autobody foam too, @oldlady It sounds like the same type of foam and you can have bigger pieces when needed.
Most ceramics should be double boxed except little things like mugs. I've not had anything break since I began doing that. I'd rather make it bomb proof than have to remake a special piece. If you have more than one item, wrap them individually and then wrap them together so they don't move at all. It's them clanking together that will break them rather than force from outside the box. I use rubber bands, bubble wrap or kraft paper to bind them. Before you seal it, shake the box. If you hear anything, add more stuffing. 2 inches of insulation all around, and under a little pressure, so it's like a jack in the box when you open it.
I bought boxes from a local manufacturer that is a 10 minutes drive from me. That way, they don't need to ship them. They have other supplies as well, like kraft paper, tape, etc. I don't use Uline because I don't support their political views and there are lots of local places to get supplies around me. I bought boxes because that way I don't have to try to scramble to get ones to nest in each other. Also, they are just the sizes I want, so I need less packing material inside them. Other than that, I haven't bought any shipping supplies except tape. I will switch to paper tape once my plastic tape runs out, that's a good idea.
I try to remember the three R's of recycling: reduce, reuse, recycle. Right now everything is shipped, so it's hard to reduce the amount of stuff we're using, but the next step is to reuse what's already here instead of buying something new unless that's the only option.
I've also thought about adding a note in there, along the lines of "Packed with reused/recycled materials, please keep the cycle going by reusing or donating" It may spark somebody to think about it! I wish they could donate it back to me!