My nana lives on SS only. I call her every night before she goes to bed. At 94 one of the highlights of her day is going over what she's eaten that day and what she's planning for tomorrow.
Breakfast is usuall eggs & grits, oatmeal, toast, yogurt (she buys the expensive Greek kind because she likes it best), omelets, blueberry pancakes (she still makes them from scratch) or French toast.
She generally eats breakfast late because it takes her a while to make her bed, take her shower, take her little chihuahua out, etc., so she doesn't generally eat lunch but snacks on things like pepper jack cheese & crackers, a cup of yogurt, whatever.
Dinner always includes some kind of meat (usually whatever her dog, Sammy, will eat because she's always cooked for him...he's never had a piece of dog food in his life), chicken, beef, liver, whatever. She also has vegetables or fruit and a starchy vegetable (her beef & noodles are yummy...it's the only time I eat noodles), potato, rice or noodles. And she usually has some kind of dessert (coconut macaroons dipped in chocolate are her favorite).
As she doesn't even feed Sammy dog food, she's not going to eat it either. So, obviously, you can eat quite well on a fixed income. Of course, she doesn't go out the day she get's her SS check and buy expensive steaks, wine or beer, sodas, chips and other crap.
Cindie