Teaching 'drop it' and 'take it' is one of the very first things we teach. It is a matter of respect when it comes to dropping things to you on command. He needs to learn that all things belong to you - even if he found them first.
First, put your dog on the leash (for control) then get a stick or stiff toy at least 6 inches long - not a soft toy he can get a grip on or food he can break off and swallow. Start with an object that doesn't have high value to him and work towards an object that does have high value. Food will probably be the toughest challenge as it is easy for him to just swallow it and win.
Offer it to your dog and say 'take it' in a happy tone. let him chew on it for 15 seconds - do not let go of the item. Say 'drop it' short, sharp and firm in tone. Almost startle him with the command as you point quickly at the item and his nose. The startle alone should impress him. If he lets go then praise him and gently stroke his face and head. If he does not let go - ask again and vibrate the item in his mouth moving towards the back of his mouth. This should be strong enough to make him want to let go, but not so strong to hurt him. When he releases be very pleased and praise & pet.
Repeat this - holding the item and sharing it with your dog for longer times each round. As he gives willingly then allow the item to be his for just a few seconds, keeping your hand close by and then move your hand in and ask him to 'drop it'. Again increasing times until it can be his for five minutes and he still drops it nicely to you. Working him in his normal obedience commands just before you do this can help. It places him a submissive role and makes him more agreeable over all and ready to be more cooperative.
Practice a lot when you are just hanging around the house - get him to drop dozens of things throughout the day, don't wait to teach it when you need it and don't avoid teaching good manners like you did today.
This command is serious enough to save his life. What if it were a pill you dropped? or a big chunk of chocolate?
Love Them & Lead Them,
~Elizabeth & Doug
Dog Training the Way Nature Intended