Diapers- bring about 1.5x the number of diapers you would normally use. That way you have extra if needed. Consider buying overnight diapers for times when you may not have the ability to change the diaper every 2-3 hours.
Wet wipes: bring a full container of these. These are not only good for diaper changes, but also for little messes that may occur.
Remember to make a list prior to travel. This will reduce the chance that you forget something important. But even if you do, there is always a store where you should be able to find something comparable.