You can give either the regular schlarp or the crunch cookie to the wizard. There is different dialogue depending on which one you give him. Once you've given him one, you cannot give him the other and the candy bar is forever doomed to sit in your inventory uneaten.
You can give the lettuce cube to Orbo if you don't have the dark ham in your inventory and haven't already given it to him. He'll stand on top of it.
I don't think the brand of ghat does anything other than showing that you've already been killed in the homicide valley and can't go back in again.