1. Open up all the pdf files with the Preview app (which is the default and native OSX app for viewing pdf files).
2. Select one of the pdf files to use as the main pdf file into which you will merge pages from all other pdf files. From this point forward, I will refer to this as the base pdf file.
3. View the "Sidebar" by clicking on View --> Sidebar in the top bar menu.
4. Select one or more pages within the Sidebar of another pdf. You can hold down the Command key in order to select multiple individual pages within the Sidebar or Press and hold the Command and A keys to select all of the pages within the Sidebar.
5. Drag and drop the selected pages and position them where you want within the Sidebar of the base pdf file.
6. Repeat steps 4 and 5 for each additional pdf file to merge into the base pdf file.
7. [Optional] In order to not tamper with the base pdf file's contents, save the base pdf file as some new name.
That's it! Enjoy!
Update: Since this post, I have discovered that you can merge just about anything that the Preview app supports into a PDF file. Very nice!