Walking is definitely a great way to get some cardio in, and lifting light weights at the gym can be a good way to build some strength. If you're considering adding more Gym Equipment to your routine, I would suggest talking to your doctor or a personal trainer to make sure you're using the equipment safely and effectively, especially if you're preparing for surgery.
As for the drinks, they can be a good source of protein after your workout to help your muscles recover, but it's important to also make sure you're getting a balanced diet with plenty of fruits and veggies. Keep up the great work, and best of luck with your weight loss journey!