Dan,
Here is what you do...relax, and don't worry about it. Your hard work in training up until this point is what's going to get you through the race, not special protein powders or specialized training sessions.
-What to eat the day before, well, you will want to change up your diet slightly the week prior, eat more carbs that fiber. You will want you your diet to be 60-75% carbs, white rice, pastas, etc. Now don't load up on additional foods, just make healthy choices, you body needs nutrition, not junk carbs. I like to eat walnuts(stored energy in the mono's and poly's), carrots(potassium), salted peanuts(sodium, vitamin E), the week prior. These are my snacks, not meals. Absolutely no fiber the night before or morning of, unless you want to spend your warm-up in the porta-john. You will want to eat your breakfast about 3-4 hours before your event. Maybe a power bar or something t like that 2 hours before your event and sip on some carb sports drink that morning, I like pedialite, its for children who suffer from dehydration due to dissentary, but it has tons of key electrolytes, way more than any sports drink you can buy. Keep in mind that the thing you eat and do the night before you race will have little effect on you performance, so load up(nutrition/hydration/sleep) the few nights before the race. Make sure you are going #1 every 2-3 hours(a decent amount), and that it is slightly yellow but not too dark or clear, if this is the case, then you are properly hydrated.
-For warm-up, I am pretty sure you will be able to get in the water, if not do a few sets of a couple push-ups(3 or 4, you don't need to do a whole lot, plus if you do, it will really tire out your upper body) followed by some stretching of the upper body. Remember this is not a duathlon, I always see people jogging to warm up for there swim??? Thats great that they just got all the blood flowing to there legs, now try to swim, good luck. Trust me on this.
-Hopefully you have experimented in training with your nutritional needs, this is an essential part of training. It greatly depends on your specific needs, there is nothing set in stone as far as nutritional needs goes except that you will need to replenish electrolytes through out the race. If you have not done this yet, then I would reccomend a semi-solid(gel, cliff shots, blocks), during the bike leg, and try to hit the aid stations during the run for electrolytes. Other wise, you can start testing some foods/supplements during training so there are no suprise's on race day.
-You don't need protein powder, just a balanced diet, I drink milk after my long sets to recover, with some natural PB as well.
-1 key work out you must do is a taper week(cutting back your training load by about 75%), the week leading up to your event. Don't try to sneak any ground breaking work outs in order to build confidence, you will just wear your self down and have a crappy race. Remember too that fatigue has a latency period, so during taper phases you will feel very tired and sluggish, this is perfectly normal. If you taper properly, this fatigue will be gone when it comes time to race and you will be very fresh and ready to go. Don't give in to temptation, resist the urge to go a little faster or longer during taper just because you think you are losing your fitness(your not!), you will thank yourself on race day.
-1 last note. Train like you will race, race like you have trained.....and have fun! Good luck, see you there!
-Anthony