It's an interesting question. I discovered in high-school that an avid interest in science expressed through reading back issues of national geographic, popular science, and other similar magazines can give you a significant leg up (giving me a lot of advantages in biology, chemistry, physics, mathematics, and computer science).

In some ways a lot of what's available online for free is better (wikipedia is generally better than most physical encyclopedias, not least because it's so fast to search), but in some cases there's still a gap. There are plenty of bite-sized nibbles, but there aren't as many cohesive, well put-together larger bites of knowledge such as you'd find with popularized science books and magazine articles.