We carried an older exposure suit on the aircraft I flew in. Fortunately, I never had the “opportunity” to use one in the ocean. That would not have been a good day.

There are options other than the Stearns model. WestMarine's float coats & work suit page might have one that would work. Obviously the full suits would be warmer than a float-coat, but not conducive to all day wear. Any might be good for throwing in the trunk with other gear. No first-hand experience with any of these.