Where would you place files included in a script placed in /usr/local/bin/ on Ubuntu?

Where would you place files included in a script placed in /usr/local/bin/ on Ubuntu?

And would you put your own scripts in /usr/local/bin or elsewhere?

I don't really have a specific problem, for now I will just put all the files in /usr/local/bin even though the included files will not be needed to be in path. Would just be neat if there was a convention for this.

It's for Perl and bash scripts if that matters.

Edit 1: So I googled a bit and came to the conclusion that my use of /usr/local/bin for my own system wide scripts may have been misguided [1, 2] and that it might be better to put them in my own directory, like /usr/mystuff/bin/, and just make subdirectories for included files there.

Edit 2: After looking in the FHS I have now concluded that I will use directories under /opt/ for my own system-wide scripts. The FHS says about /opt/:

The directories /opt/bin, /opt/doc, /opt/include, /opt/info, /opt/lib, and /opt/man are reserved for local system administrator use.