Can I? In a backpack, shoulder bag, tennis racquet bag etc??

I do have a CWP.

legally/technically yes.  Be ready to do a lot of splanin.

790.06 enumerates the weapons and firearms that may be carried.  Since an AR pistol is, well, a pistol then your are good.

790.221 prohibits short barrel rifles so be ready to explain why your "gun" that looks like a SBR is really just a pistol.

With the recent rewrite of 790.01, you should be gtg even with a rifle or SBR but in either case, you may need a  good firearms attorney to explain it to the judge.

The answer is yes.  Assuming you are placing your Sig Brace on an AR pistol, not an SBR or rifle.

However, should you need to use it to defend yourself or others, you need to remember not to shoulder it, or it becomes a rifle. Carrying a rifle concealed is illegal, as is having an sbr that isnt registered. You'd be screwed in many ways.

Hahaha.

http://www.floridaconcealedcarry.com/Forum/showthread.php?54482-Concealed-rifle-carry-in-bag

Lotta people believe carrying a rifle, SBR/Suppressor is legal based on the wording of the law, worst case is it's a $25 administrative fee.

That's the very last thing in the world I'd worry about "remembering."

worst case is that you may find yourself face down on the  pavement, a knee in your back, 'cuffs on your wrists.  THEN, after all that gets sorted out, a $25 administrative fee.  

Isn't there some clause in Florida law regarding if a firearm is used to prevent a felony that the person using the firearm cannot be charged with a firearm crime? If that exists (disclaimer: I'm not a lawyer and I've been drinking), I'd assume it'd protect you from FL firearms charges, but I dunno how Holder would handle it if the "victim" were a misguided youth attempting to turn his life around.

In aviation, you keep a bass line running in your head with decision making about how the NTSB report would look based on your decisions. I would think that an AR pistol with a sig brace would be best kept as a secondary weapon and not one's only option if they thought they'd need to pull out a gun. I also think it would be more difficult to disarm someone with a sig brace.

No.
What you might be thinking about is immunity to prosecution in the event you use deadly force if that force was required to defend yourself or others when you have a reasonable fear of death or great bodily harm; OR to prevent the imminent commission of a forcible felony (if that felony provides the aforementioned reasonable fear of death or great bodily harm.)

For example, if you are carrying concealed without a license and you shoot an attacker, you'll likely get off on the Discharge in Public/Improper Display/Agg. Assault/Agg. Battery/Manslaughter charge but not the the carrying a concealed firearm (felony) charge.

If that happens record everything during the encounter and bring that video to a good lawyer.  Just as it's said your average Joe cannot use ignorance as an excuse for not knowing the law, neither can an LEO, even more so for s trained LEO.

Personally, I would leave the AR pistol in the vehicle and carry a good capacity handgun, like a CZ.