First album that I bought with my own money: In-A-Gadda-Da-Vida by Iron Butterfly
First 45RPM single that I bought with my own money: Lady Godiva by Peter & Gordon
First CD: (I can't remember, but there weren't many available when I bought my CD player back in 1982)
First prerecorded videotape: Xanadu (starring Olivia Newton John)
First Laserdisk: Xanadu (do you see a pattern???)
And yes, I ended up buying Xanadu on DVD when it was released. When I was in high school, I used to buy prerecorded reel-to-reel tapes. I even joined the Columbia House tape club just to have access to more 7" tapes. I still have the tapes, but nothing to play them on. I assume that the tapes are probably no good by now with lots of print through and oxide shedding.
I can truthfully say that I have NEVER purchased a prerecorded cassette tape. I've seen too many tapes eaten by car cassette players. I'd rather buy the album/CD and make my own tape.