My boys love these books about animals and adventure:
Ernest Thompson Seton animal books (Wild Animals I have Known, Wild Animal Ways, Monarch the Big Bear etc.)
Jim Kjelgaard’s books as previously mentioned
Call of the Wild
Jules Verne’s Journey to the Center of the Earth, Around the World in Eighty Days, and Twenty Thousand Leagues Under the Sea
South by Sir Shackleton (my boys love reading this…my ds7 loves it on audio) about Shackleton’s expedition to the Antarctic, losing his ship Endurance, but saving all of his men
Robert Louis Stevenson’s Kidnapped
The Hobbit and The Fellowship of the Ring Trilogy