What would you do with a solution to 3-SAT?

I'll tell you what I'd do, man: two chicks at the same time, man.

<insert standard disclaimers and preemptive apologies here>

Anyway, my actual answer would have been about the same as jimrandomh's, but, assuming I'm the only one who has the polynomial-time solution to 3-SAT, in the absence of sufficiently specific knowledge about how to create an FAI, I would use it to make huge amounts of money (either by using it to get a significant advantage in prediction and using that to play the stock market (etc.) or just by making super-useful thitherto-impossible products or services using it) and then use that to support said universe-optimization efforts.