There are several, including the Federal gun free zones, e.g. Court Houses, Post Offices, military bases, etc.
The school one is not absolute. If the Principal gives you written permission, firearms can be taken onto school property.
I love the “Securely Tied Package” option…. I purchased a used handgun from Meltzer in Garfield a number of years back. No box he just put it in a thin food store type plastic bag and handed it to me.. So I asked “Is this legal”. He said, “Oh no absolutely not”and grabbed the bag back from me.. I assumed he was going to get a box or some sort of case to take it home in…. Nope… He simply looped on carry handle under the other and handed it back…. Saying with a smile. “ Good catch the package must securely tied”