There are several ways to secure turnbuckles for your shrouds and stays. Cotter pins and wire locking rings are commonly used to secure turnbuckles. They are small and difficult to get a hold of. If you are like me, more often than not, they end up overboard from klutzy handling. Of course you have an endless supply at your disposal - not! This results in an extra trip to your local marina supply at the most inopportune times. I know, keep two of everything.
Here is a method I have used for the last couple of years.
Buy a pack of stainless steel welding rods(wire). This will be a life time supply for you and your sailing buddies.

Cut a piece with wire cutters or my tool of choice, needle nose pliers.

I usually estimate about 2 - 3 inches longer than the distance between the holes you are inserting the wire into.

Make the first ninety degree bend about 1 to 1 1/2 inches from the end. Place the wire up to the turnbuckle and make the second bend equal to the distance between the holes. Insert the wire through each hole.

Once the wire is through, bend the end of the protruding wire into the turnbuckle so that it will not catch on you or your sails.

This is quick to install and remove, easy to grasp, and has less of a tendency to end up in the water!
On flights to paris as well as flights to phoenix the staff is friendly enough to repeat the directions twice. However if you are unable to close your seat buckle, don’t count on help if you are aboard flights to florida or worse, the flights to canada.