Before surgery I tried to get prepared by buying some foods such as baby food and chicken broth. I landed up not using it and it went to waste. This was because of two reasons. My taste buds changed significantly after surgery and I could not tolerate those foods. And secondarily, after surgery the amount of food I was eating was incredibly small. During the first 8 weeks, my meal volume was 2 ounces (4 tablespoons) per meal. Take out a 1/4 cup measuring cup and look at how small that is. That is the meal volume.
Prior to surgery I was constantly hungry. Even when I was eating a meal, all I could think about was what I would eat for my next meal. After surgery (when I reached the solid food stage), I completely lost my hunger. So it was not difficult to lose the weight when I was not hungry.
The three most important elements after RNY gastric bypass surgery are to meet your daily protein, fluid and vitamin requirements. Food is secondary because your body is converting your stored fat into the energy that drives your body. Thus you lose weight.
Weight loss is achieved after surgery through meal volume control. You begin at 2 ounces (1/4 cup) per meal and gradually over the next year and a half increase the volume to 1 cup per meal. With this minuscule amount of food, it is next to impossible to meet your protein daily requirements by food alone, so therefore you need to rely on supplements such as protein shakes.
So it might be unwise to be too prepared. The key is to experiment after surgery. Since your taste buds may change, experiment with the various formulations of protein shakes. You do not have to like protein shakes but you must be able to tolerate them until your meal volume rises to the point that you can met your protein requirements by food alone. Sometimes you can buy a variety pack of protein mixes at GNC. Also be willing to experiment after surgery to find fluids that you can tolerate. When I was in the hospital right after surgery, I couldn't even drink the water because it tasted overly chlorinated like swimming pool water.