Some inconsiderate boor packed soda into their checked luggage. It opened during the flight, and leaked not only all over their stuff, but down into DH's luggage below it.
It ruined a lot of clothes, caused us to miss an entire day of vacation to file claim forms (airline never did give us a cent--they went bankrupt in 1991ish) and replace clothes and luggage. What it didn't stain it covered in sticky soda goo.
If you really have to... at least wrap it in several layers of lawn bags and tape them tightly sealed shut with packing tape.
Karen--not sure how you are getting to WDW, but why not take one of the excellent car services that will make a free grocery stop for you, and buy your soda as well as other snacks there? I recommend Tiffany. They'll cost a few dollars more than Mears, but you'll be treated like royalty, and won't have to stop at 4 other hotels on the way to drop off other guests.
It would certainly be cheaper than cleaning or replacing clothes if the soda leaks.
With the cost of machines and soap powder, it's $5 per load at WDW resorts.
Anne