I remember once getting a demo CD for strategy games (not a cereal box one but one they had for like $5 beside the cash register at computer stores). It set a trajectory on my life that resulted in my later WoW addiction.

That disc had Dune II on it, the first RTS game I ever played. I was instantly hooked. Then I tried Warcraft II (also on that disc) and it was even better. I mentioned it to a friend at school and he had just gotten SC:BW, which meant he had two play discs and let me borrow the SC disc first, then the BW disc later and we played a ton of StarCraft. Somehow, on battle.net despite using the same key (my assumption is they screwed something up in early manufacturing and duplicated some keys, which meant they couldn't just limit it to one player online at a time per key for some set of keys that included my friend's).

That eventually led to me discovering the StarCraft modding community, which defined my later high school years. Funny enough, I wasn't even into modding that much, I was more fascinated with the tools that enabled it and the reverse engineering process involved in building those tools.

It also led me on my path to D2, WC3, SC2, and finally WoW (uh, might have the order wrong for SC2).

I wonder how things would have gone for me without that demo disc.

It was expensive in most parts of the world, though.

Those ones above were all included with windows back in the day, like installed from the disc when you installed windows, then they'd be discoverable in Start -> Programs -> Accessories -> Games (other than paint, which was in accessories) IIRC. Eventually they moved it out of the accessories folder, then later on they changed which games were included, eliminating some, though these ones I believe remained the longest until MS started instead advertising games they had on the windows store.