What in your opinion in the best practice in Laravel to adding small, custom classes? I've seen and used a "library" folder in app. Of course, anything that is going to be larger than a single class would be abstracted into its own package.
I don't personally use a "library" folder. Instead, I'd create an "app/*" directory that corresponds to whatever it relates to. For example, I have a number of email-specific classes for Campaign Monitor. Those go in a "app/Emails" directory. Keep it simple.