I have a taken it as far as Avignon. Buy a little food before you get on the train at GDN, you can buy something to drink on the train. I got some wine of course. Nice ride through the countryside chewing on your baguet and sipping a little vino, seems very civilized.
Nicer to pack a good picnic before you board with good bread, cheese, fruit and whatever you fancy. You can pick up some little 250 ml bottles of wine at a supermarket, and some nice bubbly water, though of course those will be available on the train, at a premium.
The train goes VERY fast, so you won't see as much of the scenery as you might in a slower train, but still very pleasant and so much more civilised than contemporary flights.