Hi!
Le Sac was given away at Essen, I believe in either 2001 or 2002.
It was after the first expansion(s) to Carcassonne were released, and people could start to notice a difference in colour on the backs of the tiles when they were stacked up (as per the rules of the base game). So to avoid people being able to see/predict the next tile, Le Sac was introduced as a way to avoid that, and randomise the drawing of the next tile.
Not sure how many of them were released, but it is one of the rarest collectors items in the world of Carcassonne today.
Later they included a bag with expansions, as the idea was well received and more and more used.
Here's a recent picture I took of my Le Sac, in comparison with the bag that came with the first Russian Promo set and the Travel edition: