How do I clean my mac out into a hard drive, and then access files from a new mac?

I would like to empty all my MacBook Pro's information into an external hard drive, not just backing it up, but completely emptying out my internal hard drive. I am planning on getting a new computer, and I would like to access those files from the new MacBook. However, I do not want to migrate all the files back to my new MacBook; I would just like to access my photos and documents directly on my hard drive, if possible. On another note, is it possible to divide a hard drive so as to perform this function (having files that are not in my computer), and using it as a time machine to back my new computer up as well?