The straw idea is great for chained necklaces but if your jewelry is beaded or has a chunky design to it a toilet paper or paper towel tube works as well. With the tubes, depending on how thick the design or beads are you can fit several necklaces or bracelets around the cardboard.
Personally I went to the dollar store and picked up a coupon folio that is like a little file sorter. This way I can put one piece of jewelry in each pocket (there's like 12 of them) poking the earrings through the tabs on top then folding it closed to have everything in one place. It fits nicely in my carry on and if I happen to leave the folio in plain sight no one thinks twice about it perhaps assuming it's a receipt holder.
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