And end up with this:
It only takes 3 bottles and you're this guy
I previously wrote about this same topic here and here, and those posts got a lot of traction, so I thought I'd write an update on what I've figured out since.
-how to carry sufficient liquid for a long ride or endurance race, as well as your flat kit and food, all without spoiling your aerodynamics.
- a between-the-aerobars front bottle (bottle 1), seat-tube mounted bottle (bottle 2), behind the saddle rear bottle (carrying flat kit), and an aero bento box behind the stem (nutrition).
You really only need two bottles-worth of liquid for any race distance. With aid stations about every hour on the bike it's easy to simply refuel as you go. I saw a lot of individuals at my recent half-ironman sporting 3 to 4 bottles on the bike (1 up front, 1 on the frame, and 2 in back in a "bottle-launcher" ie a side-by-side rear seatpost mounted carrier). If you're racing on your own liquid nutrition (like Infinit) and want to carry it with you, then this works, but it otherwise seems over the top since you can easily swap bottles out.
In choosing the up-front bottle, I went with a between the aerobars bottle rather than one of the aero solutions. I did get a Torhans AeroZ , which, after just a few dates, I'm very impressed by. It seemed to me the best engineered of the products available in its category, but I hadn't used it often enough in training to decide to race with this season. TriRig does a nice review of this product category. The plus side of products with a straw is that you need only duck your head down to sip from them, you don't have to ride along and pull your bottle out to sip. The downside would be managing to refill it quickly (and without substantial spillage) at each aid station, and also not being able to see how much liquid you've taken in or is left.
To keep things simple for training, so I can easily start with my bike bottle, and racing, so I can easily swap out at aid stations, I use a zip tied cage between my aerobar mounts. Works great.
For my second bottle, I'm currently simply using a downtube bottle. Purists will contend that the thick, round bottle ruins the aero seattube and wheelcover benefit, and maybe so, but it's convenient and I'm not riding at speeds faster than 25mph for races anyway. The next step would be to swap out my behind the saddle flat kit (below section) for holding a bottle of liquid. I've seen many pros recommend the Xlab Gorilla cage as strong and tight enough for the task. But it's also $50. For now I've been happy with a seat tube mounted bottle.
For my flat kit, I've worked out keeping my spare tube, tire levers, and Topeak Minidual pump in a Specialized bottle carrier (with the top open), held together using electrical tape. It works great, and is fast at hand in case I do flat. Having your flat kit encased in tape wrapped up beneath your saddle, if it takes you 5 minutes to get it out, could be a little counter-productive. It's easy to simply zip-tie the bottle cage to rear saddle rails. It fits snuggly there and keeps things tucked fairly nicely out of the wind.
Another option would be to carry the second bottle for liquid behind the saddle where my flat kit is, and use an aero option, say from Torhans with the VR Tool Carrier version (Specialized has their own product), to carry a pared down flat kit with a CO2 minipump, tire lever, and spare tube. AeroGeeks did a nice write up on this option.
The easy choice for nutrition is to use an aero-bento mounted behind the stem. I like my DarkSpeedWorks Speedpack (aero bento box). It easily fits the gels and powerbars I use for my nutrition on long course bike legs. It's shaped to keep its form despite being stuffed with GU, and adds a nice trailing edge to the otherwise round stem.
So there you have it, a fairly streamlined, utilitarian option for carrying your liquid, food, and flat kit in training and racing. With the aerobar mounted bottle, behind the saddle flat kit, and aero bento box, just about all of my nutrition and gear is tucked away from the wind. My seat tube mounted bottle disrupts airflow over the back half of the bike, but it is dirty air and it's a price I'm willing to pay for convenience. I'd otherwise recommend looking at aero seat tube mounted options for a flat kit, and carrying your second bottle in tight bottle cage behind the saddle.