Deciding on where to pack certain items can be a confusing process, but when you are traveling by air it is important to pack certain items in your carry-on bag.  It doesn't happen often, but baggage does get lost by airlines from time to time, necessary items like medication as well as medication and travel papers should be either kept on the person or in the carry-on bag.  This way even the most brief separation with your luggage won't cause either medical or identification problems.