There’s a good Printemps department store (Rue Nationale). There’s a medium-sized Westfield shopping centre, by Gare Lille-Flandres. I don’t think anything is particularly cheaper.
Prices in France, like the UK, seem to be rising gradually. So don’t expect too many bargains.
If you smoke, cigarettes can only be bought from the tabacs [Plus the ‘Relay’ shops/newsagents in the stations; one after security at the Eurostar terminal], plenty all over the place, but many of them close quite early. If you have time and transport, they are €8.70 in Belgium (€11.50 in France).
Lots of places in France close on Sundays (and often for lunch). For example, lots of the shops in Lille don’t open on Sundays.
Some other shops. If you fancy taking home a fine bit of French knitwear (in particular), Saint James in the old town (Rue Esquermoise) is your destination! For cheese, Fromagerie Philippe Olivier (Rue du Cure Saint-Etienne/Rue Basse) is part of a small chain. And very, very good! (there’s also one next door to Calais Vins, if you’re stopping for Duty Free; and a very good patisserie). There are loads of fine food shops dotted around the old town. Books and stuff: Furet du Nord, Place General de Gaulle (who incidentally was born in Lille, but the birthplace museum is a bit rubbish!). Quirky shops: H Huret (guns/knives/etc), Loisiers Scientifique (models), Royez Musique (musical instruments).
If you want to pretend you’re French, forget the berets and onion strings, and buy yourself a JOTT lightweight puffa jacket! One shop in Westfield another in old Lille. Everyone seems to have one, including me!
Chocolate is a bit of a thing here. There are lots of chocolate shops, from the chains such as Leonidas and Jeff de Bruges, to spectacular independents such as Maison Georges Larnicol (Rue Esquermoise).
Relatively recently, lots of tinned seafood (!) shops have appeared. Packaged in very colourful cans. People seem to like to give them as gifts. There are a few, including la belle-iloise on Rue Esquermoise.
Supermarkets. You’ll find plenty of Carrefour/Auchan/etc dotted around the centre. Smaller versions of the big ones further out. There is one (that I know of) very large supermarket, which is Carrefour, at the back of the Westfield mall, by Lille-Flandres. There’s a weird Monoprix/M&S joint venture in Gare Lille-Flandres. Prior to the ‘B’ word, it was a full-on M&S, where I got my bacon from (French bacon is rubbish!), but no more! Beer (on promotion) is often very cheap in supermarkets. Do not be tempted by French supermarket sandwiches, uniformly inedible. Supermarkets tend to be closed by around 10pm. No 24 hour ones that I know of.
Lille RWC Guide 