Wrapping the item
Wrap each panel in several layers of bubble wrap or corrugated paper, then add a layer of foam board insulation at least 12mm on each side.
Make sure you have padding (bubble wrap, corrugated paper, or foam sheets) between each item. Then make sure they are fastened tightly together in one bundle. Make multiple nested pieces into one big unit, then wrap that so it's well padded.
Ship stained glass panels in a wooden crate. Make a wooden box and line it with foam, on all sides. The ends of the box should be of substantial timber, making the box at least 100mm (4") thick. Use lightweight, thin wood, but stiff enough that it remains durable. Screw wood on the front and back of the edge of the framing timbers. Fill the space so the glass is in the middle of the box. The most important thing is to minimise flex. You also must minimise shock from a drop.
Line the box in bubble wrap or corrugated paper. Put a layer of filler in the bottom.
Set the piece in the middle of the box, then fill all around with more filler. Press the filler firmly so the packaged items can't move and shift in the box. Allow at least 50mm of packing around the contents and ensure the contents cannot settle through the box filler perhaps by placing a cardboard pad on top of the fill before placing contents in the box.
Filler is material that will fill the space between the wrapped items and the sides of the box. This can be shredded paper, bagged peanuts or foam sheets. Bubble wrap with peanuts is sufficient, but don't use peanuts unassisted. They have a habit of vibrating off to one side of the package, leaving the cargo unprotected on the other side. Mix the peanuts with either wrapped newspaper or excelsior (shredded paper) or place them in numerous small bags so they can't shift.
Many people double box everything. This involves putting the boxed items inside another bigger box. Suspend the inside box within a larger box, bigger by at least 50mm on all six sides. You can use cardboard strips to make an 'X' to put in the bottom and top and small pieces of foam on the four sides to keep the inner box from shifting. Fill the spaces in between the two boxes with something that will absorb shock or impact, like shredded paper. For a very fragile piece the outside box might be made of 6mm plywood.
One caution on packing: Don't overdo it. If you force so much packing material (peanuts, bubble wrap, etc.) into the boxes, the whole thing (inner and outer box) becomes a solid mass and the force may still transfer to the piece and break it. When packers say "float," they mean it. You want enough packing material to hold the stuff in place well, not so much that it becomes part of the piece.