The first record I bought myself was Alpha Centauri by Tangerine Dream. Other early buys are hazy, but could also have been debut LPs by The Clash, Elvis Costello, X-Ray Spex or Tom Robinson Band. All had to be replaced over the years after teenage wear and tear, the vulnerability of LPs and my heavy-handed handling took their toll.
I would have bought 7" too but would not recall which.