The husband suggests eating _____ this evening.

The correct choice emphasizes the preference for staying at home rather than going to a restaurant or dining away from home. "Eating in" is a commonly used phrase that refers to having a meal at home, suggesting a cozy or relaxed atmosphere. This choice aligns with typical conversational contexts where individuals discuss plans for meals.

Using "out" would imply going to a restaurant, while "for" and "by" do not fit grammatically or logically in the context of the sentence regarding meal arrangements. Therefore, "eating in" is the most suitable option.