I've used my Ralph's card at Food 4 Less. They advertise ecoupons in the store and suggest you add the offers in the app before buying the items on signs throughout the store.
For the items I buy regularly (peanut butter, soda, english muffins, cereal, paper goods) Ralphs is cheaper. Baking supplies are almost always cheaper at Ralphs too. Other things like yogurt, almond milk and produce will depend on a sale. I have 2 Ralphs, a Vons and a Pavilions about the same distance, so I default to Ralphs. But on vacation, I don't really care if I spend a few dollars more on some items for convenience.
OP, will you have a car and what are you actually looking for? If it's just something like milk and bottled water, there's a CVS on Harbor and Katella. If you have a car and need specialty items, consider going farther to Trader Joe's or maybe Sprout's (would recommend this for GF). Otherwise there's a Ralphs on Chapman just east of GCH and a Vons on Chapman west of GCH, both are about the same distance, and reasonable cab fare or rideshare.