Always freeze your gel packs for at least 14 hours in a domestic freezer before using them in your medicine bag. Always keep your cooled medical bag closed unless you need to access your medication. Never place your medication in direct contact with the frozen gel pack.
Take care not to drop or bump the cold packs especially whilst frozen. Plastic becomes brittle when frozen and so any impact could result in a fine crack that won't necessarily be noticed straight away. Then once the cold pack starts to thaw, the gel will leak into the pocket of the bag. Try to freeze the cold packs on a flat shelf or in a container in the freezer to protect them.
It's strongly advised to travel with a copy of your prescription and a letter from your GP with details of your medication (including its generic name, not just the brand name and the name of the health condition that you need the medication for). As well as helping you avoid any problems at customs, this will be useful if you need medical help while you're away. It may be worth getting the information translated into the language of the country or countries that you're visiting. Always seek advice from the airline you are travelling with or the departure/transit airport authorities regarding travelling with cooled medical bags or cooling devices.
Equipment and medication shown in photos is for illustrative purposes only.