I like what you've got so far OR. My Pop's side of the family were farmers, and they all did heavy manual labor starting at age 5. Didn't stunt their growth any, all of them are well over 6 feet tall. Prepared them well for football and military service as well.
Some other things that might be fun to add in
Hay Bale toss (or equivalent.)
Hand over Hand pulls (with sled)