Means of signaling have been suggested.

OK a couple of commercial PFD's also.

But you don't want to be obvious. You don't want to be singled out on the beach. Who goes swiming at the beach in a lifevest. Even one that is uninflated.

You have a pocket. Why not put a couple or three 1 Gallon Zip Loc bags in your pocket. Then if you need floatation Simply inflate and zip shut you have a pillow of air.

So you can only use 2. One under each arm. Why did I suggest 3? Depending on the time you need you might lose one. Or one could get a hole in it while stored in the pocket. You are not going to remove and replace them every swim session. The third is sort of an installed spare.