One usually relies on the airlines to provide life jackets when one is flying, but those traveling to regattas (in New Zealand for instance) might need to take their own. In this case if your jacket is the inflatable type you need to declare its compressed air cylinder to the airline ahead of time. Karen Corbin has provided the following example of such a declaration (made to Qantas).
To: firstname.lastname@example.orgShe received the following reply.
My travelling companion and I will be travelling from Hobart to Melbourne and return, each carrying a pfd with co 2 cartridge. This will be in checked luggage.
Our reference is ABC123. Flight JQ123 28th Jan and JQ456 9th Feb 2016. ...
An approval document has been issued and attached for your travel. This approval is valid until 31 December 2016 and should be kept for future trips on the Qantas Group, including Jetstar. Please ensure you keep this in a safe place and carry it with you whenever you travel. When checking in please declare to the customer service agent that you are carrying a self-inflating life jacket and show them a copy of your approval letter. ...