I remember my first comic so clearly: Issue 21 of Marvel Comic's late 1970s series Godzilla King of the Monsters. I purchased the comic at a 7-11 just down the street from my grade school, turning in enough refundable coke bottles to cover the 35 cent price.
The title on the cover reads "Godzilla battles the raging might of Devil Dinosaur in The Doom Trip." I read that comic until it literally fell apart. While it wasn't a comic masterpiece, I fell in love with both comics and fantasies from that point on.