Delia has an awesome suggestion of how to kill some time near the Gare du Nord in Paris if you need to: the Marché St Quentin
Last time I had some time to kill was when heading to Munich by sleeper train a million years ago. That time, I walked from the Gare du Nord to the Gare de l’Est – it’s really not at all far – and spent the time on the terrasse of a street café having a steak-frites and a carafe de vin rouge.
Niles's Blog 
It is awesome: they’re used to British tourists, so the cheese is done in sealed packs and so forth.
And there’s a convenient branch of Nicolas just down the road for all your plonk needs.