Should I use my own package?

[Gribouillis]

Everything that you can do to make your programming more comfortable is good. The issue with creating your own utility package is not forgetting the standard library, it is to create a dependency of your programs on this utility package. It means that if you want to modify the utility package later, you'll need to care about backward compatibility, and if you want to detach your programs later from this package, there will be some work here too. That said, as it will increase your productivity today, go for it.