Just my opinion but saltines and melba toast would make me FEEL deprived which is a ticket to failure for me. I usually buy some really tasty, grainy bread for my carbs OR add beans with fibre and also protein. Protein consumption seems to be a key to feeling full. Some people eat too little. Beans are a great combo food. I get a can of red beans, cook them with some onion and garlic, smash them and add some salsa and cheese for a really tasty and full of fiber/protein meal. If you use low fat(not no fat) cheese, it's very low fat as well. No fat cheese has a rubber/plastic texture so I just can not eat it. I also extend my salad dressing by measuring a serving-2T usually-and mixing it with equal amt of non fat plain yoghurt. Gets in some calcium and gives you a decent amt of dressing. One more thing. Add flavor with things like cinnamon, lemon juice, cumin, basil-thyme-rosemary-oregano-parsley. The flavor of a fresh herb or spice really lifts your spirits and adds nothing to your calorie count. I grow a container garden and bring them in when it gets cold so I have fresh herbs year round.
Why are you limiting your calorie intake to 800-900? 1200 is a healthy count and with a little exersize you will still lose weight. Add 300 calories a day and take a 20 minute walk or do some stretching. Your body will shut down because it thinks you're fasting and it wants to hold fat. I can lose weight on 1500-1800 if I step up my exersize to 4 instead of 3X a week AND the calories are healthy foods, not junk.