rain gear waterbottle stash

A post on bikeforum mentioned waterproof pants that "roll up to the size of a water bottle." This gives us an idea for a convenient place to store emergency rain/slush/snow gear on our bike. Since water bottles are usually empty during the winter anyway, why not stash a cheap poncho and rain pants inside for unexpected bad weather?

We haven't actually tried this out, but it seems like it would work. Perfect for those of us who don't do so well planning ahead.

Other stuff that might fit in there:
-plastic shopping bags to protect valuables from unexpected showers
-spare tube or patch kit
-if the bottle has a wide mouth, you might be able to store your mobile phone or ipod inside (padding recommended).
-emergency hot chocolate/chicken soup money
-dry socks