the abasto mall has a kosher mcdonalds next door to another kosher mall type fast food joint.
in palermo neigborhood next door to the chabad there is a pizzeria/italian restaurant called el pasaje which is next door to a meat version. both are very expensive geared to tourists. around the corner is a kosher sushi place Tib Tuna at Argerich 404 and down the block is an ice cream parlor called Persicco at salguero street which has kosher flavors listed on the menu.
Parrilla Al Galope is the most famous grill house and they take credit cards. it is located in the "once" neighborhood at Tucumán 2637 [Tel. 4963-6888]. a block away is Restaurant Mamá Jacinta at Tucumán 2802. you can walk around the neighborhood and find lots of groceries, restaurants and bakeries.
and if you eat vegetarian, there are some actually terrific vegetarian [not hekshered] restaurants to recommend.