Definitely get the injection kit.  My daughter was diagnosed a non salt waster as well and years later the endo said that she was sure she must be a mild salt waster! (That is another whole story - I suspected that all along and frequently voiced my opinion!)   We have used the shots only twice and probably should have the 3rd time when she just somehow unknowingly became dehydrated - no apparent illness.  That time we rushed her from the dr office to the hospital and they administred the solu-cortef in her IV.  Also, be sure that before any surgical procedure or before your child is ever put to sleep that they are given Solu-Cortef.  I practically had to follow a dr into the OR once.  Apparently no one had paid any attention to the big red bold letters on her chart that said she must have the Solu-Cortef prior to and during a knee operation!  In short, do anything you must to insure your child’s safety.