What are the best foods to consume on 900 calorie diet?

Fruits, veggies, lean protein (soy, chicken breasts, fish)

I have to tell you though, if this is for a diet, you should really look into how your personal metabolic rate works. If you dip too low (typically below 1200 calories) your body begins to go into starvation mode, hence you store everything you eat. If this is something recommended to you by a doctor, then my previous answer still stands, but I would talk to a nutritionist before beginning any kind of extreme calorie diet (on either end of the spectrum). Check out TheDailyPlate.com to track calories though. It provides the nutritional content for almost any food you could think of!