I'm still a newbie myself, so always learning.
Extra bottles of de-chlorinator -- in case you have to add water back due to a leak...
Extra pump [you've mentioned]
Maybe somewhere to move the fish if needed, like a large kiddie pool or stock tank.
Air pump & tubing.
Some on here have given a recommended "first aid kit" so if someone will re-post that information, it would be helpful. I don't know how much "first aid" is a necessary EMERGENCY item, though. Depends on the emergency and how much you know about what to do.