I was going to say “keep it in the realm of possibility,” but I know that means less when it comes to Trump. I’ll trust you to know what I mean.
Mine is: subtly hints to followers that they should dox a questioner he believes is a Clinton plant.
Ok well this is at least slightly feasible but I admit highly unlikely. I would love to see Trump lose his stack based on a bait from Clinton, take a few threatening steps towards Clinton and then go down under a pile of secret service bodies.
Well I can fantasise can’t I?
It’s cute how you’ve suggested that Trump could do something subtly. 
Perform well.
Walk out in the middle of the event, waving his hands and shouting that the whole thing is rigged against him, and it’s DISGUSTING.
Hey, it’s not outside the realm of possibility that he could do something “outrageous” and still be considered to have done well.
I’m skeptical it’ll happen, but it’s possible.
Walk out in frustration in the middle of the debate.
I also had the same exact fantasy coremelt. 
That’s actually a little disturbing that more than one person thought of it. Yikes!
It’s not particularly outrageous by his standards, but looking at the video of his ‘apology’ (which was filmed in a controlled environment), he is going to be 100% vitriol. He’s going to be a 4Chan troll made flesh, without the benefit of anonymity.
I think he’s going to focus more time on Bill’s behavior and imply Hillary condoned it. But who knows at this point?
Grab Hillary by the pussy.
Oh, I forgot another I thought of: make some kind of insulting reference to Anderson Cooper’s sexuality.
He’s going to take a lot of swipes at Bill, but at least half his ammo is going to be aimed at Republicans who have been “disloyal.”
Raises an interesting logistical and procedural question.
Is there a Secret Service protocol for what to do if two protected people get into a physical altercation. Do their respective SS details have to duke it out as well?
Remind people he’s a Democrat, and a Democrat who has donated to HRC campaigns in the past.
I’ve been hoping for a gun fight between the SS factions with Trump taking a random bullet or maybe twenty.
Tempting, but I’m guessing that each team will just grab its candidate and pull him or her off stage.
I think he’s going to say "I said some bad things but your husband raped people and you supported, so what’s worse: my words or your deeds?
And depending on his delivery I could actually a scenario in which that might win some viewers over. If I’m on Hillary’s prep team, that’s what I’m preparing for.
I’d also be ready for Bengazi. There were a few hanging curve balls in that first debate that were right over the plate and Trump could have crushed if he’d been more disciplined.
If I’m Trump’s advisers, I keep it simple. You know he’s not going to prepare so limit his prep to a few key talking points that he can go back to again and again. And regardless of the question asked, find a way to work it back to those points.
National security question? Hillary created ISIS and got 4 diplomats killed in Libya.
Terrorism? There was no ISIS before Hillary.
Don, aren’t you a pervert? Maybe so but her husband’s a rapist, and she defends rapists/
Did’nt you guys have a President who espoused and executed the same philosophy as the Donald, and who is now in prison?
I honestly believe Trump spent yesterday rubbing his hands together in glee when each new GOP Representative or Senator or Governor or Cabinet Secretary announced that he’d finally proved himself to be a candidate they couldn’t support. “Outstanding,” he must’ve said; I can’t imagine how swiftly the Democrats will desert Crooked Hillary following my delivery of that game-changing sentence at the debate!"
Moshe Katsav. Although, to be fair, he wasn’t directly elected by the public.