The only things I ever put in my dogs' crates (pups and adults) were kongs and a nylabone - they can't easily destroy either of those so I never worried and they were/are kept occupied.
I've never used puppy kongs though - I always use the red ones for pups as they work just as well and are sturdier. When they hit about 10 months to a year of age (depending on the dog and how strong/hard of a chewer they are), I switch to a black kong simply because I've had two adult dogs split the red ones (appropriately sized for their breeds, too).