Lego is always a great option - it's fun and also educational. They have some great sets with cool themes that most 8-year-old boys would enjoy.
For books, it really depends on his interests but some popular choices are often fantasy-themed or adventure stories with plenty of illustrations to keep them engaged. Perhaps consider classic tales like the Hobbit or Greek myths - they're adventurous, and also educate him about different cultures and history.
You could also look for activity books that combine fun and learning, like maze books or search and find books with facts alongside the puzzles. Or how about comic book series like Bone or Calvin & Hobbes, which are fun reads with some subtle lessons too.
If he's into science, then there are some great kid-friendly experiment kits that teach him about chemistry or physics principles in a hands-on way. Or go for a cool robot building kit - again, lots of learning but they're tons of fun too!