If you have the room I'd say not only bring the sheets but as much of the contents of the pack-n-play that you can fit in your luggage. If there are toys or mobiles or anything else that hangs on the pack-n-play at home, try to bring it. Your 1 year old will likely be much more comfortable and sleep much more soundly the more WDW's pack-n-play looks like the one at home.