Save the PDF of the final version (from the journal's website) in a folder you keep of everything you've published. Mine's called my-papers. Ideally this folder is in the cloud, backed up somewhere.
Look at the copyright form you signed. See what you can put online. Sometimes it's nothing, sometimes it's the final version, sometimes it's a penultimate version. If you can't put anything up, skip this step. Use Acrobat Pro (or something else) to put full citation information on the paper itself (if you can't readily tell from what the PDF already has) and save it (my-papers again).
Print the paper and put it in a binder called My Papers. You know, in case there's an electronics apocalypse.