When I was in 5th grader in 1969ish, we were given a book club magazine and was allowed to order my first book. I loved that book and it gave me the love of reading sci fi and fantasy. Unfortunately, the book was destroyed with my whole collection of about 1000 books that I had placed in storage by mice. I can not remember the title or the author. The story line was about a post apocalyptic world where a teen boy and a mutant cat (the size of a lion) were traveling together and came to a forbidden city (like New York), with falling buildings and mutant humans. I would love to be able to read that book again now.