Shortening substitutes for pan greasing
Shortening is used here because it is solid at room temperature so it adheres to the sides of the pan and provides a better barrier. Spray oil can do ok and has emulsifiers in it to help it along but solid fat works better.

An obvious substitute is butter. Actually butter can be substituted for shortening in a lot of applications (with the exception of when the shortening is being used for its high smoke point.) Some saturated fats, like coconut oil, might have more flavor than you want.

If you are looking for more convenience- they make non-stick spray that has flour in it as well exactly for this purpose.