One change I made to my racing a few years ago that saved me a lot of time and reduced stress, was to always have my bike setup as I'd race it.
A lot of athletes I know leave it to the last minute to get their bikes race ready. This is an even greater issue for the athletes that understand that there is an optimal and sub-optimal way to attach all that you need during a race to your bike. I've been there myself and have witnessed many of my clients making last minute setup decisions.
Other than a few minor adjustments, my tip is to always run your race setup. Running your race setup will ensure that what you determine as aerodynamic is also functional.
Do you know that they bottle cage you just mounted behind your saddle works?
Here is what I do...
Flat Kit: I fold a clincher tube with a removable valve core (butyl - CO2 will diffuse through latex) along with a tire lever, valve extender wrench, and wedge it under my saddle.
My CO2 and shooter are stored in the Xlab stealth pocket behind my stem. I carry an allen key set in my jersey pocket when I train, but would have room for a few small keys in the pocket if I decided to carry them.
Bottles: I run one bottle between my arms and one on the down tube or behind the saddle when I race. For training, I'll typically run 3 bottles so that all I have to do for racing is remove a cage.
Wheels: I train on a set of 303 carbon clinchers. One of the great things about the advancement of clincher technology is the option to train on race wheels without worrying about wearing out your expensive tubular tires.
I race with an 808 front and rear disc that are of similar widths as my training wheels. This saves me from having to adjust my brakes which can be a real struggle depending on what bike you have. There are some bikes where you need to remove the crank to adjust the rear brake.
I know this is not a cheap option, but this technology has been out for several years and I'm sure there are some good deals out there.
If you follow this simple advice, your bike setup is easy and can save you from wigging out in your hotel room the night before a race.