My husband uses a CPAP, and has recently taken to bringing his own extension cord. As bige does, he also has the documentation in the pocket, and -- just in case -- carries a note from his doctor that simply states its medical need. He was questioned about it once last year, and these papers enabled him to get through with no problems.
I don't know what kind of water you use, yet my husband uses distilled water. Our TA calls ahead to arrange for a large bottle to be delivered to our cabin upon embarkation. On some lines, we're charged a few dollars, but it's better than lugging something else along.
As for our medications, we keep them in the original bottles. I also bring along the info sheets we get from the pharmacy as it shows the name of the medication, prescribing physician, and any contraindications. I pack this separately from the meds.