In goaltending the difference between making the next level or not is usually decided by you athleticism. We call this the athletic separation. Goalies that are more fit will usually tend to do better and it is more attractive towards the coach. The more fit you are the better you will perform because you will not run out of energy so fast.
Some ways to stay fit and ready for hockey is to do some sort of cardio approximately 3-6 days a week. You can do things like: running, biking, rollerblading, elliptical etc. Another key factor is to make sure you are eating healthy. Try and cut out the food that are not healthy and substitute it with some fruit or something healthy. Make sure you are drinking lots of water everyday so that you stay hydrated.