TL;DR
Packer/unpacker buildings to pack (small) specific numbers of items together into a single item.What ?
The idea is that you can prepare exact combinations of items for a recipe in one location, and then ship them somewhere else to be crafted. The goal is not to increase the amount that can be transported, so packing will be limited to a small number of items (say 8).Packing must always be done via a "packer" building, where you can specify the combination of items you want in each "crate". Unpacking will be done by an "unpacker inserter". This will work a bit like the burner inserter: it will first take a "crate" and place it onto itself. The crate will be opened and then the individual items will be inserted into the destination one at a time.