Quote Originally Posted by GingerbreadGirl View Post
...seat bag for tube and tools and cell phone and in this heat I have been wearing my running tanks instead of jerseys (don't have a sleeveless jersey yet) so I've been carrying a tiny drawstring nylon backpack. I freeze my second water bottle and throw that in there so my back doesn't get hot, and have my id and a snack in there. A shot blok or maybe one of those packed lunch-sized potato chips.

I am trying to figure out how to squeeze another water bottle onto my road compact... do those cages with the velcro strap really stay on? What if I reinforce with zipties?
I assume you already have a cage on the seat tube. Will another cage not fit on the downtube? I have a Bontrager cage on my MTB's downtube that offers a "side entry." If a standard cage won't work, you might try something like that.