Most passenger jet planes travel at too high an altitude and too fast a velocity for the average “jumper” to successfully escape and deploy a chute, even with experience. You don’t see recreational parachute jumpers jump out of jet planes now, do you? And that stunt that Schwarzenegger pulled in that spy movie, plain smoke and mirrors…Military jet pilots who eject in almost every case will lose consciousness in this rapid decompression and acceleration, as the body and brain can’t handle the stress; their chutes (in their seats) are set to auto-deploy if they make it to that altitude with vitals intact.
As for the floatation device option, even if a plane was able to make a controlled, minimal speed landing on water, you’re still talking an impact velocity exceeding 200–250 miles per hour; strapped to your seat with an ordinary lap belt, what do you think the chances of surviving an impact crash at that speed would be? Most crash test dummies test at speeds below 50 miles per hour, with a very high probability of critical injuries when speeds exceed that (without additional restraint such as an airbag).
If I were in that scenario, I would want to “pleasantly” lose consciousness well before impact; perhaps a dose of something ‘special’ that has a rapid-release response may be in order. Sorry to be a killjoy to your question/discussion.
P.S. as for the surviving and shark situation, check out the movie Open Water.