For my experience with Cessnas, if you have hit so hard to deform the fuselage to the point where the door cannot be opened, you probably did not survive. My friend crashed his 150 so hard, that it stopped in less than a foot. The coroner later told us that he had experienced a 200G stop. I opened the door, and another firefighter opened the other door with no difficulty during the rescue attempt. This is not an argument against popping the doors open before crash landing/ditching (as some POH's say to do), but rather a suggestion not to fixate on it. Some of the Cessna doors will re latch if pushed closed. If the Cessna you're flying has an "open/close/latch" position, and you want to keep it opened for the crash, after it is opened a little, move the lever back to "latch" and if will not latch closed again when pushed.
Know your seat belts. A very few [now] Cessna still have the shoulder harness which clips over a pin on the lap belt tang, which is left to right reversed. Thus, undoing the lap belt leaves the shoulder harness to remaining lap belt still connected diagonally across your torso. In this case, undoing the lap belt which hanging will not release the shoulder harness, and you're not getting out, unless you wriggle out, or cut the belt. I have found a few errant Cessnas like this over the decades, and referred them to maintenance before flight to have the belts corrected. The very oldest Cessnas had metal to fabric lap belts, which would not release under load, or when wet. These have been AD'd out, and I haven't seen one in decades. But if you see one of these, refuse the plane until it's corrected.
If you're ditching, do so parallel to the swells, regardless of the wave and wind direction. If you're flying such that ditching is a possibility, you should be noting the swell direction as you would note forced landing areas. You want to know that before you need it! And, note the compass heading to be flying to be parallel to the swells, as you may not have any other [shore] visual reference to do it. If the waves are the height of swells, you should not be flying single engine there. The land equivalent is hitting a bump on the runway (which, yes, could be damagingly large), compared to flying into a shallow hill. The plane may push through the wave, but it will come to a sudden stop in the swell.
Always be actually wearing your lifejacket, and if temperatures dictate, an immersion suit. "Having it aboard" is totally useless if you're not wearing it. If you doubt this, take the dunker course, and you won't doubt it after that! Wearing my lifejacket literally saved my life.
Take the dunker course, it's way fun, and confidence building. My experience having taken the dunker course, and teaching water rescue for years was a major factor in my own survival after a water crash.