Think of something specific that he did for you recently. Did he take extra time to sit and talk with you or grab an extra blanket out of the closet for you last night? You can also thank him for something that he always does, such as being willing to work so hard every day.
Tell him you miss him
Let him know that he's important in your life and you look forward to seeing him.
Who doesn't love an unexpected compliment? You know him better than anyone, so compliment him on something others don't notice about him.