Thoughts:
spare gas in bottle? (bottle $10 gas $4 getting home safe? Priceless)
Not having ridden any jet skies (though I'd love to try once), I am still pretty certain that their cargo capacity is virtually nil.
My impression is that jet skis have the serious drawback that if you loose engine power your only option is to hang around while slowly sinking, hoping and praying that you'll be rescued before actually sinking, drowning or becoming hypothermic. Jet skis probably won't become submarines, but will sink partially - and make a really lousy life raft. Plan accordingly.
Evidently, he did have several backup plans for motor failure, including radio and flares. Those failed him. Electronic gear fails. A PLB as a backup to his radio would make very much sense. So would not riding alone. But having a backup plan, including water proof radios, flares and such makes him miles beyond your typical incompetent merciless-lost-at-sea nilly-willy.
Although I don't consider jet skis seaworthy vessels, I am in no position to say that he shouldn't have done what he did. We need to appreciate the fact that some people will accept higher risk levels than others. I'm fine with that, as long as they don't whine about it when things go wrong. He clearly doesn't sound like a whiner to me.