If you want to bring your mom back a box of fancy chocolate from your latest adventure, and you don’t want to bring it into your carry on (because you are afraid that you will eat it in the middle of your long flight home) it is perfectly acceptable to pack it away in your bag. The temperatures at 30,000 feet in the belly of the plane is quite cold and will keep your chocolate nice and cool on their ride back home. Soda, on the other hand, may not be such a great idea. Your checked luggage is going to be shaken and thrown around a lot by the people loading it up onto the plane, and a can of soda might explode under those circumstances. It would be a terrible thing to arrive at your destination only to discover that all of your clothes are covered in diet soda.