Other monks have doled out excellent advice (as usual), but I thought it might be worth emphasizing the fact that storing homemade routines in separate files is exactly what modules are for. You say I understand that this is what happens with modules. I think where you misunderstand is that you may not realize you can make your own modules very easily. This is exactly what all the other monks are giving you advice on how to do.

(Hopefully my post doesn't come off sounding too condescending; I am just trying to explain a connection you didn't seem to get when you posted your question.)