A lot of people that have sent me eggs in cartons have either wrapped the eggs in a small piece of bubble wrap, or they use toilet paper or paper towels. Some even use wood shavings. The key is to make sure the eggs don't move around inside the carton! If they bump the top or each other, that's when they crack. I have never had luck sending eggs in cartons, but have received many in cartons that were just fine. I prefer to free float mine in the box, individually bubble wrapped, then wrapped together with bubble wrap, with shredded or crumpled paper in there, or packing peanuts, if I have any.