I bought a Stanley thermos and a Camelbak water bottle, and I estimate that I've saved about 1000 coffee cups and about 2000 water bottles in a little over a year's time.
I travel a lot, and I live in Starbucks for their internet connection and also and have to be outside to work on wireless networks with public safety and service provider companies. Water bottles would (literally) fill the floor of passenger side of my rental car every time I took it back to the airport (it was a running joke with the National Car dudes at several of the main airports I'd hit).
Buying water and coffee is extremely expensive while traveling. I went from $2 a cuppa coffee to like 36 cents at Starbucks with my gold card (they just refill it now without asking me, I'm such a regular at the locations where I travel) and I easily saved anywhere from $1 to $4 on each bottle of water (depending on where I'd get it; airports are hella expensive, and I spend 1/5 of my week in an airport quite often).
(Granted, I never had to pay for any of these expenses, it's still kinda nice to look back and think of how much I'm saving.)
On a somewhat related note, I recently used a bidet at my friend's house last week in San Francisco. He is an energy analyst (pun intended) for the city, and one of my best friends who was always the butt of our tree hugger jokes in high school. They cost a fair amount money (like $100), but the amount you save on toilet paper makes it a wash. (ok, I really gotta stop now...I could go on forever, do not encourage me!)