Oxnard is not as ritzy as some of its neighbors. The shopping is far more low key. Two Farmers Markets (Channel Islands and Downtown Oxnard) keep everything very home-grown. Expect to find citrus fruits, strawberries and artichokes at the booths, along with flowers. This is a very agriculturally rich area.
If you're visiting the waterfront, stop by Oxnard's Fisherman's Wharf for some lovely seaside shops and boutiques in a fishing village style.
Or stop by the tree-shaded Oxnard Esplanade or The Rose for a more typical shopping experience.
If you still have a shopping urge, drive to nearby Ventura for a number of very nice shopping venues, from Ventura Harbor Village (as much entertainment and boat center as shopping hub) to its eclectic Main Street. Camarillo is a good place for more bargain-centered malls, such as the Camarillo Premium Outlets.