Drop it is good, fortunately my dogs just seemed to already know that one without being taught. And you can teach him "leave it". This is how I was taught how to teach my dogs leave it. Have him on a leash and have some treats in hand. Drop some kind of food pieces on the floor in front of him and tell him leave it. Walk him past the food and if he tries to grab it, get between him and the food stomping the floor and telling him "leave it!". (This will work best on a hard surfaced floor.) When he stops and looks up at you, give him a treat. Eye contact is always important. When you can walk him past food successfully without him grabbing it, you can have him sit and stay, drop some food in front of him and step back. Tell him come and leave it and he should walk past the food and straight to you for a treat. If he tries to grab any off the floor, do the same stomping and leave it.