This is what I did to lose 30 lbs in 30 days before my surgery: I would have a protein shake for breakfast, another for lunch, and a hearty (ultra low carb) dinner. I started May 11th while I was still working (teacher), and kept at it until my surgery on June 19th. Altogether, I'd lost 32 lbs by the day of the surgery. The first 3-4 days are rough as you detox from carbs. By day 4, you should start to feel really good. Your mind is clear, your joints don't hurt as much, and your energy is up. You even get better sleep!
A typical dinner while pre-op dieting would be 4-6 oz ribeye steak (cut up and dipped in A1)
Or I would cut up 4-6 oz of rotisserie chicken and throw it into some cream of chicken or chicken broth. (Like chicken soup, if you will)
I'd even eat a cheeseburger (without the bun, or course). If you have the space, eat a double! I'd been sleeved 14 years ago, so I still had restriction.
My 16-year-old daughter was inspired and dieted a bit with me. She's doesn't have any type of bariatric surgery. She was losing up to 5 lbs a week just by cutting carbs. She would have bacon and eggs with cheese for brkfst, she'd have a shake for lunch cuz school, and she'd have hearty, no carb dinners as well. Detoxing from carbs REALLY helps. Drink 5-6 bottles of water a day. Have all the sugar-free jello and sugar-free popsicles you want. They're considered clear liquids. You can even start taking bariatric vitamins before your surgery to make sure your getting everything you need. Wish you the best of luck!