Nutrition, hydration, and more questions (HIM) - your help is needed and appreciated!

Bike:
1)  However you prefer to carry the equipment you need.  I've taken to using a bento box this season vs. a saddle bag in prior years.
2)  How heavy is a tube & CO2?  How pissed would you be to be stuck because you screwed up your spare and spent your CO2?
3)  Sorry, don't/won't use one.

Run:
1)  Jersey pocket.  Pick a flavor you can stomach warm.

Swim:
1)  Not if they want to move through T1 quickly.  Most tri jersey's are sleeveless and are supposed to be worn under your wetsuit.
2)  305 is not waterproof.  Don't wear it on the swim.  I don't use mine at all durinag a race.
3)  It's not my race.  Decide how you want to pace yourself and plan accordingly.

Short answer to most of the questions:  You should be doing at least some of your training with the setup you think you'll be racing with.  That goes for bike, nutrition, and apparel.

Longer version: You not only can, but probably should be working out some of these answers through training.  A perfect example is the issue of how to carry stuff.  Well, what pockets will you actually have?  Different manufacturers have different pocket configurations on both tri shorts and tri tops.  Some of your options will be limited by what you wear.  No reason not to be trying out carrying gels in your pockets for a long brick, for instance--esp. if you have a particular reason for "nightmares" about hot gels--and seeing how that goes for you on the run.  And better sooner rather than closer to race day where a botched key workout becomes a bigger loss.

Anyhow...a couple specifics...

I'd carry two CO2 cartridges.  For an HIM, I carry one spare tube and a mini-patch kit...I'll roll the dice on a 56 mile ride that if I happen to flat twice, I can patch one of the two blown tubes.  Not so much a weight issue for me as a space issue.

Gels for run in pockets (I wear Zoot tri shorts/top that have two pockets in each).  I actually put them in prior to the swim and forget about them.  Only thing I add in T1 is plastic coin purse with some salt caps and ibuprofen that I throw in a tri top pocket at that point.  Nutrition for bike in bento box.

I do like to wear my Garmin 205 at least for the run (helps keep me from going out too fast, which is always a problem for me)...typically I turn it on before the race and either strap it on my wrist as I'm heading out of T2 or (for longer races like an HIM where I'm less concerned about a few more seconds of transition) in T1 (so I have data from the ride for my log).

Your other questions, it seems to me, anyway, are a matter of personal comfort level and habit and you should be determining by your experience in training.

I like the quote in Triathlon Canada this month where Lisa Bentley talks about carrying fluids on the bike.  "A lot of people worry about all that weight on my bike, but without my fuel, my bike isn't going anywhere."

I figure the extras are kind of like that.  I'm planning on carrying an extra tube and a patch kit plus all my fluids.  It's not going to matter - it's my first race and I would rather be over-prepared than not-prepared.

I'm also planning on practicing filling my aero bottle on the fly.  I imagine I'll enlist some help from family members and a quiet stretch of road so that I can practice grabbing bottles, filling and dumping them...

Bike:
1) I leave mine on, I just may not take all the bottles. It's a pain to take it on and off and I'm not fast enough for the extra weight to matter. You have to carry the tubes/tools so do what is easiest.
2) I carry 1 tube and 3 CO2s, figuring if I pulled a Chrissie Wellington I'd have back ups. I'm not the swiftest tire changer.
3) Yes, practice filling from other bottles and be ready to grab a bottle at the exchange, put it in your aero and then toss it before the drop, or you can fill from your downtube, grab a bottle at the exchange and toss your downtube bottle. It's up to you.

Run:
1) For an HIM run I only need one gel and I put it in my back pocket. As others have said, I too like a warm gel so it doesn't bother me.

Transition:
1) I'm not a guy but I'd wear the top under the wetsuit. You don't want to be screwing with that in T1.
2) Garmin's aren't waterproof so if you want to wear it, turn it on in the morning and get a signal, leave it in transition and grab it on the way out of T2. You may not get a signal immediately but it will pick up soon enough and you can still use it for general pacing.
3) I train with HR for pacing so I wear my HRM. I also like the HRM since the Garmin isn't waterproof, however I'm planning to put my Garmin on in T2 at my HIM this weekend since I tend to go out way too fast off the bike and pay later. If you have trained with the strap you won't notice it during the race. Just use some BodyGlide.

Good luck!

Thanks so much for all the advice!

Just one note on the garmin thing. I'm not planning to wear the garmin during the swim. I'm planning to leave it on my bike ready to go. What I was asking about was the velcro strap (the thing on the right):

Photo didn't show up for me, but you're referring to the HRM strap I assume. I'm guessing it's ok in the water but I'd check with Garmin if I were you. They haven't made anything waterproof until the latest models. I bought a Polar for that reason alone, I want something I can hit start on at the beginning, stop at the end and monitor my HR along the way.

Ah, sorry about that the pic disappeared:

Bike: I don't have the x-wing so my stuff is in a small saddle bag. I've had problems with flats before so I may be a bit paranoid about it. It's been good for a long time now but I still carry two spare tubes and a frame pump. A few ounces less doesn't seem to help when I've had to carry the bike and my aerodynamics are terrible with the bike on my shoulder. I recently tried installing an aerodrink thing on my aerobars and have practiced refilling it from a downtube bottle while riding. I'm still undecided about the aerodrink, but you should be as adept and flexible as possible with whatever equipment you're using.

Run: I've carried a gel in my shorts pockets before but at the last half IM I just used what was on the run course. Someone else suggested a jersey pocket already. If none of that works for you, maybe consider some kind of running belt pouch. I have some belts that my wife will borrow and use without the water bottle sometimes, but I think some of the systems have belts where you could hang a just a pouch if that was what you needed.

Transition: After my first tri, I bought a tri top (sleeveless) and wear it now for the swim whether I'm using a wetsuit or not. I wear the HR monitor chest strap through the swim all the time and put the wrist monitor on during T1. At my last half IM, I turned on the Garmin305 before the swim started. It was synced up and ready to go in T1. I don't pay a lot of attention to the HR reading during the race but if I want to check it for any reason, it's there. At my first half IM, a hot one, an unexpected high reading tipped me off that I was behind on my hydration before I felt it otherwise and probably saved me from a DNF.