Prepare for It. Like the situation above, you should go into the conversation knowing how you'll respond if your boss asks you to extend your notice. If you've landed another job offer and have already set a start date, this may not be possible__so practice sticking to your guns: "Because I have a new opportunity lined up, my last day here is firm.
The Hand_off. Finally, state your willingness to help out with the transition. You don't need to go into great detail (and definitely don't promise anything you can't deliver), but a couple of lines stating that you'll ensure a smooth wrap_up of your duties will show that you're in the game until the very end. Obviously, feel free to adjust this a bit based on your experience and your company culture, then submit it via the typical procedures at your company.