Mönchengladbach is not about big shopping tours and never will be, try Düsseldorf, Cologne, Venlo NL or Roermond NL instead.
Anyway, there are some shops worth being mentioned:
If you like german bread: Cafe Ã, Marktstieg 8, Very close to the "Alter Markt", is a non-chain-bakery and cafe. They do "handcrafted", organic, whole wheat bread. That's what germans miss when they're abroad some even prior to beer.
If you consider tea bags a crime and are in need of the real stuff: "Tee Gschwender", Hindenburgstr., at the "Theater Galerie" will give you sweet relief.
You'll find a Chucks and Vans shop at the Theater Galerie, too.
If you're into Punk, Hardcore, Ska etc. music and clothes, pay a visit to Nightmare Records, Waldhausener Str. Altstadt. edit