If you have two puzzles of different sizes, you can often pack them both in the same box and save a bundle on shipping. Here is an example of the process starting with two different sized puzzle boxes...
Remember, no matter what put the puzzle pieces in ziplock bags! If the larger box has a lot of room, you may be able to just skootch all the pieces to one side and set the smaller box inside. But most times that isn't going to work. So what I suggest is to take the pieces rom the larger box and break them into two or three bags. You may need to place one of the bags inside the smaller box. In this case, I would suggest taking the lid off the smaller box and placing it upside down on the bottom of that same box. This way the person opening the outer box sees all the puzzle bags. Also, put a slip of paper in each of the bats to let the other person quickly see which bags go with which puzzle.
For the above example, one of the bags from the cat puzzle had to go inside the smaller box just to make things fit. This seems a little weird but really, once packaged up it looks very sensible and easy for the person receiving the puzzles to figure out.
Finally, put the lid on the larger box and tape it closed with a couple small bits of tape. The lid most likely won't fit all the way down but that is ok.
At this point, you wrap up the box just like you would a single puzzle. For wrapping instructions, see the article "How to pack your puzzle for shipping". By shipping in this way, you reduce the overall size of the two puzzles and that drastically reduces the cost. In case you are wondering, shipping this puzzle all the way across the country only cost $9.51 by purchasing a discounted shipping label on PirateShip.com. (Sept. 10, 2020) If shipped individually, these same puzzles would have cost $8.53 each. So I just saved $7.55 by shipping them together in one box. Keeping the overall size low made the biggest difference.
Today, I received two puzzles packed into a larger box. I was curious how much would be saved by packing them both into the same box, wrapping them in brown paper instead of another box and shipping them back to the person that sent them to me. Of course, I didn't actually ship them, but I did price the labels.
They came stacked one on top of the other inside a box that was turned inside out (clever idea). The outter box was 15" x 13" x 5" and weighed 3.8 pounds.
I was easily able to scoot all of the puzzle pieces from the larger box to one side and drop the smaller box inside. This new configuration was 15" x 10" x 2.5" and weighed 2.9 pounds.
These puzzles originally went from Ocenside New York to me here in Salem Oregon. Using PirateShip.com to generate the labels going the other direction, the original box priced out at $18.96 and the repackaged box was only $13.25. This is a savings of $5.71 (as of Feb. 10, 2021). This demonstrates that it pays to pack your puzzles in the smallest box you can.