Difficult. And so many answers, mostly starting with, 'it depends...!'

A useful exercise is to play 'if everything that can go wrong does go wrong, what does it look like...' eg. You don't sleep a wink, your swim goggles fall down the portaloo just as you release your morning poo, you tear your wetsuit, you have three punctures, you loose your nutrition etc etc. Then you can work out what you'd do to either prevent these things happening, or how you will deal with them when they do. And then decide how far you go, balancing with your race goals - so you may decide that you'll go equipped to deal with two punctures, and after that your chance of a placed finish are gone anyway, so you'll just wait for the service van and enjoy the rest of the ride as a scenic event.

Here's my recipe - and it may not be to everyone's taste, but it works for me. I have a Shiv which has a built in hydration bladder, and a 'fuel cell' which has enough space to carry some basic tools and some grub if needed.

I fill the inbuilt bladder with water (750ml) and top it up as needed at the aid stations. I grab a banana from the stations whenever I feel the need for something solid.

I use infinit for my nutrition, so it's all liquid. So I have an x-labs superwing hanging off the back of the saddle, with two gorilla bottle cages (because they're one of the grippiest cages, so less chance of my bottles flying out). Up till now, I've put enough infinit to fuel the whole bike leg in those two bottles, marked them in 20 min increments, and supplemented with water from the bladder (as the infinit mix is too concentrated for optimal absorption if I put 5-6 hours worth in 1.5l).

I carry two inner tubes, minitool, two tyre levers, an x-lab inflator, and two CO2 cylinders (inflator and CO2 hang off the back of the superwing). I have ENVE 8.9's, so I carry one additional valve extender with valve installed, and a bit of plumbers tape already on the valve stems of my inner tubes.

So, puncture 1 - tube out, attach extender to one of my new tubes, re-inflate. Jam the old tube in the wing (it has space in the middle, and you must not litter on an IM course). Puncture two, I need to grab the extender from one of the damaged tubes and put it on the new tube. Two CO2 cylinders should do for two punctures, or one puncture and cocking up attaching the cylinder and loosing all the CO2 ;)

One thing I'm toying with is just carrying one bottle of infinit for the first half the IM, and having the other in my special needs bag. I usually need to pee and stretch at around 100km anyway, so it wouldn't be a problem to swap bottles then as well.

Remember that on the full IM, you can put an extra set of spares in your special needs bag, so if you're unlucky enough to puncture early, you can then grab fresh supplies when you pass SN. You might decide that one extra tube is enough.

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Ironman Certified Coach
Legendary Camel-Spotter

bernmc covered it pretty well from an intelligent approach to decision-making to his own choices. Read every ST thread you can find with race reports for IMAZ from competitors of similar front pack ability and pick up on patterns like punctures from goatheads etc. Don't let the weight of an extra water bottle concern you in the least on that course. Make your decision based on it's necessity (or not) and it's aero impact in the potential mount location. IIRC, you've not yet gotten 2015's bike crash out of the way, so unless you handle that at the upcoming half, maybe carry a couple bandaids. (-:

Tubes... I've read that if you are racing latex, you should have butyl spares. The CO2 leaks faster in latex.

Nutrition... This is my setup. 3 hour Infinit bottle BTA zip tied cage. 1 water bottle in the down tube. Trash it and replace with on course water. Another 3 hour bottle (powder only) and a water bottle in special needs. I mix there. I have a bottle pod BTS zip tied cage that has 2 tubes (rear tube already has extender on it), 2 CO2s, 1 adapter, 1 tire lever and 1 mini tool.

Thanks all for the feedback....appreciate it. I'm sure I'll learn some things at Hendersen in Oct before AZ.

For IMLou I plan on keeping my 2nd Infinit bottle in SN (previously I carried it BTS). Any reason you mix there, as opposed to dropping it off in SN already mixed? Are you just worried about a potential leak while in the SN bag?

Yes. It probably would have been ok. But it was one less thing to worry about. Plus, it gave me a few seconds to chill out and talk with the volunteers. More of a mental and butt break. The water bottle was a big Dasani water. Not a bike bottle.

Let me breakdown Henderson for you...

If wetsuit, use a sleeveless, Lake Mead was boiling last year.
EASY on the bike...the hills will zap you in the heat.
Walk at aid stations on the run to get in your water/ Gatorade/ Gels. Again, hills and heat. Remember there are 3 loops. You will want to stop at 2.
Get the the massage tent asap, swear you will never do Silverman again, sign up for next year 2 weeks later.

I'm gonna have 3 bottles 400cal each on the bike and 3 more in my special needs bag. 2 behind the seat and 1 bta. I have an extender and 1 tube

I've found that heading to a catholic church and filling a bottle up with holy water helps give me a divine edge over other athletes. this is more important in full IM's. ;)

^^^^
This. And don't try to drive back to LA in Sunday night traffic post race.