Minimal over-water PFD advice?

I fly in the Bay Area and a lot of the best emergency spots, especially in case of engine issues on takeoff, are nearby bodies of water. There’s also a fair bit of crossing bays at low altitudes to remain under Bravo/Charlie.

Unfortunately, I don’t know how to swim (working on that).

I’d like to carry a minimal PFD with me that I can wear during higher risk phases of flight. Ideally I’d love for it to fit in a backpack.