Pack an extra bag in your carry on in case you're forced to check it — that way you can put your valuables in the extra bag (and under the seat in front of you).
Image from chriswaits
You never know when the airline might lose your luggage so you always want to keep your important items — like prescription medication or your camera — with you. Use the extra bag to make sure you always have access to your valuables.
A Reminder to Never Pack Your Valuables in Checked Baggage [Conde Nast Traveller]