I think I'm not explaining myself very well. No special bottle. Just think of a regular bottle of water - Dasani, Poland Spring, Aquafina, etc. Open it and pour out just a tad to make room for expansion. Close it up tightly and put it in the freezer overnight. Next morning, it's a solid block of ice. You put it in your lunch box, and it functions as an ice pack. It gradually melts, but because the water and ice is in a bottle with a tight cap, it doesn't leak, and by the afternoon it's melted enough to drink.
You can put a bottle of water into an ice bucket, but it just chills the water; it won't freeze it. It will be enjoyably cold to drink, but it won't be cold enough to keep a lunch box chilled.
Now that I know I can't freeze anything, I'll just double bag some ziplocks with ice, and call it a day.