Gluten free options in Gare du Nord

You can't get to Strasbourg from Gare du Nord. Trains to Strasbourg go from Gare de l'Est, several blocks away.

There is a Marks and Spencer inside the station should have something. Also the the Monop across the street from the station next to the Burger King might have something for less.

I also thought the train would leave from Gare del Est, but my train tickets say Gar du Nord to Strasbourg. Departing Nov. 5th TGV 2407.

Right you are. Saw this note for a train departing from Paris Est Nov 5.

Construction works are affecting railway traffic in the area Paris Est. There will be changes to the timetable of the train. A booking and reservation is therefore not possible.

So your train looks to be taking a round about way to get to Strasbourg.

From seat61 station services.
https://www.seat61.com/stations/paris-gare-du-nord.htm#supermarkets

While gluten free options are not difficult to find in Paris, I would not count on finding them at Gare du Nord unless someone has direct knowledge. This is one to come prepared with your own travel friendly food and perhaps add things like drinks, yogurt, fruit at the station.

I'd definitely shop the day before, a larger Monoprix or organic stores like Naturalia and La Vie Claire will have a good selection of gluten-free goods.