I've carried five before, but I used a rack and trunk for three of them. This was on a really hot day, lots of climbing, alone, and in an area where I didn't know if I would pass a store or not (in fact, I didn't). So what's the big deal? If you're going to need it, and you can't buy them on the go, bring them with you.

I kind of wish my current bike had a set of braze-ons under the down tube. My old hybrid did. Then at least I could carry three with regular bottle cages.

Lately I've just been taking routes where I know I can pick up another bottle at a shop along the way if I need it.

By the way, the first part of your original post speaks volumes: ...a guy passed me...

You never saw him again, right? He was faster, and didn't have to stop for refills either.