My 2 cents on hydration:

I use a behind-the-seat bottle holder (Xlab Flatwing), and definitely prefer that to the hideously ugly front-mounted systems. Yes, the front-mounted systems are slightly more convenient to use, but they tend to make your steering drift more, since you have extra weight up front. That's not a big deal when you're going straight & flat, but it would make no-hands riding more difficult, which can be important if you need to do on-the-bike clothing change, mess with gloves, zippers, food, etc. Plus, as already mentioned, they're just SO ugly. Why ruin a beautiful front-end with that ganky aerobottle? Yuck.

Rear-mounted systems become second-nature with practice, and can be accessed while in aero. But it is chiefly important that you get the right bottle cages to go with that system. The cheapie aluminum cages won't cut it, because they'll fatigue and launch the bottles. I'm using Arundel Trident cages at present, which were stupidly expensive, but have never launched a bottle in their 300-400 mile lifetimes. They grip bottles well, and won't fatigue since they're carbon.

Two bottles in the back plus one on the frame should be more than enough to get you between aid stations in any race.

I believe in keep the bike as free of junk as possible.
Have used just about everything over the years and keep returning to two bottles on the frame.
For an IM I never have more than two bottles at a time...1 bottle weighs almost three pounds...
I think getting out of the aero position to reach for bottles and moving around helps prevent muscle fatigue.... And if you spend any time reading the slowtwitch.com info on the real cost of water bottles you'll see that even the best set-up saves you a few....seconds. Prefer to go with what's comfortable.
As to food... I use a tri jersey with three pockets ( our own Trifuel top right now!) and stuff em up...maybe a bento box and thats it.
For short races..tape some gels to the top tube with electrical tape.
I agree with airborne on the front bottle business.

I actually have successfully used fig newtons as fuel in a few adventure races, and maybe one IM (can't remember). Gotta be careful on the fiber intake, but with how my body works I just need to have food that I will crave and be able to easily eat while pedaling (I don't like to single-hand ride for long).

For my Half IM I just used 2 frame mounted cages, one Endurance and one with water. My GU flask is in a bracket on my top tube. For IM, I have a Hydrotail rear mounted system (it's what Normann had in Kona) with 2 cages. I disagree that cheap aluminum cages are bad. They actually work better with the water and Gatorade bottles you will be handed on the course as you can bend the frames to clinch tighter. Carbon cages are fine for standard water bottles, but that's NOT what will be given to you at an aid station. For training long I also have a Chrono aero bottle on my seat tube. Front mounted systems just make zero sense to me. I see no great advantage and nothing but hassle.

During long rides 2.5 and up I use a aerodrink up front, a frame bottle, and a home-made hydrotail that holds two bottles, and has holes drilled out to screw in my co2 carts, and co2 microflate.

For my HIM i just use a aerodrink and frame bottle w/ my co2 and tubes on the hydrotail thingy I made.

I would say that he fig's gae me adequate nutrition in training, but during the race it was tough to keep going to them. I needed something easier to deal with. Some like a gel bottle would have been a lot easier to deal with and the aspect of NOT chewing sounds pretty good.

I tried a bunch of different products last year. What I found works best for me are the Hammer products. For a HIM I use a profile aero bottle on my bars. I fill it with water only from the aid stations. In a large (20 oz) insulated water bottle on my seat tube I mix enough Hammer Sustained Energy and Endurolytes to last 3 hours. A big gulp of this thick mixture every 20 minutes equals about 300-400 calories per hour depending on the consistency. Also by only using water in your bottle on your bars it keeps your bike from getting all gunked up with sugary, sticky liquids.

For longer training rides I'll put a second insulated water bottle behind my seat. In it I'll put Hammer Sustained Energy and Endurolytes in powder form. I'll also put a second bottle of water behind my seat. You'll have to stop about every 2 hours for water but the nutrition in these two bottles will last 6 hours.