I remember that when I was about 12 or so, I was obsessed with Lord of the Rings to the point of carrying all three of the books around with me at all times in a bag with various other things I amused myself with (yes, I was kind of painfully dorky at that age; I'm slightly amazed that I still have those books and that they didn't get stolen by one of the mean kids or anything like that). Funnily enough, I don't think I ever actually finished reading them until I was an adult (that may have been around the time that the second of the Peter Jackson LOTR movies came out).
Video games were another big one well into my teenage years (mainly NES and Super NES games); I also went through a brief period of being obsessed with pen-and-paper RPGs like Battletech and Shadowrun even though I barely understood how to play them and rarely ever got an opportunity to do so (I think I mainly just enjoyed flipping through the sourcebooks and stuff until they started falling apart).
I never got into novels, but your description of carrying around guide-type books until they wore out sounds exactly like me.
I must have gone through countless dinosaur and solar system books (among other more obscure guides, I could probably make a hefty list) that way.
I also had a Super Mario guide that I seriously loved, even though I wasn't half as obsessed with playing the game.
But I could tell you everything about it.