John Z:
You've gotten some good advice from several earlier posters. Here's my own take, for what it's worth:
1) Do not warm up at all, with any sort of jogging. You can't afford even that little bit of glycogen-burnoff.
2) Go out now just slow, but very slow. Don't have any particular finishing time in your head.
3) Whatever you think, you aren't going to run this marathon: you are going to slowly jog it, with occasional walking breaks. If you're able to do that until mile 25 without coming apart at the seams--well then, you may just be able to pick it up quite a bit in that final mile, and have the time of your life as you see that finish line coming up at ya.
4) Drink early and often. But don't over hydrate. Just pause at each water stop and get a cup.
5) Make sure you're wearing comfortable clothes. One useful thing you CAN do in the next few days is jog a mile or two in whatever you're planning to wear and making sure it doesn't chafe.
6) On race morning, if I were you, I'd tape my nipples (to prevent chafing) and smear a very thin layer of vaseline on the spot where my running shorts circle my thighs. Don't ask why; just do it. If you don't do it, of course, you'll discover why, about 15 miles in.
7) Don't assume that hitting the wall is your biggest worry. You're likely to discover all sorts of joint-quirks before that happens, assuming you jog slowly enough.
8) GO SLOW! No matter how inspired you feel, go slow. And don't assume that if you make it to mile 20 and still feel pretty good, you're home free. Respect the distance. Respect the distance. And respect it from the very first step you take. Be prepared for an odyssey. Have fun.