Dogs generally do this, trying to save excess food in case there’s a scarcity. Though most of them don’t need to do so being domestic pets, the trait had been actually handed down to them by their ascendants – the wild species of dogs.
This pattern is quite common among the predators in the wild who tend to return to their saved food for future meals. But animals, unfortunately being without etiquettes, never keep away from other’s table (or dish). Thus, hyenas, jackals, vultures and other scavengers (and not to forget their own species) always remain uncalled visitors to the predator’s unfinished prey. As a result the need to hide the left-over arose, giving birth to animal-intelligence of hiding the remains from the public glare. The concept followed and they would bury their food.
Scientists say that most dogs do this out of instinct. As is said, domestic dogs are descendants of wild wolves, who often used to come back to their left over food when they were hungry again.
But, on a lighter note, if one fine day, you find your dog burying a bone, it could simply mean that he has more than enough to eat.