Always have the essentials you need in your carry on bag.  Use the Carry On Packing Checkist and you will never forget to pack what you need. 
 
The checklist is in PDF format. You need Adobe reader to open the file. You can download and print copies on paper. Or you can open the file and click in the boxes to fill in a check mark in each box.  Once you have completed all checks you can print a copy on paper.