@christina smith,
In my garage. Hah, but I'm keeping them for myself.
Places like UHaul have many sizes of cardboard packing boxes and lots of kinds of tape. I consider that expensive, which is why I folded up my moving boxes and keep them, since I have room to do that.
Places like Target, and I suppose WalMart, have myriads of plastic storage boxes.
I've kept most of those too.
Roger is right, some "milk boxes" are fairly sturdy.