Another more popular bottle here in the USA is the Polar Bottle, better insulated than the Camelbak, holds a couple more ounces of fluid, and lasts longer too.
As far as how not to lose a bottle...hmmm, well this is sort of like losing your sunglasses, people lay things down then after a bit of time and the distraction of socializing get up and leave and forget stuff, there isn't a whole lot you can do. With sunglasses you can wear them on top of your head, or use a cord so it hangs on your neck, but a water bottle has none of those features so either leave it on the bike where someone could take it or leave it on the table in plain sight not off to the side of the table to keep it out of the way, in other words leave it in the way.