rest your head on his shoulder without making it obvious

To make it not so obvious, while you are sitting next to him, scoot down a bit in your seat, and then about a minute or more later, slowly lower your head in his direction and bring it gently to rest on his shoulder. Your guy will love it when you do this, it makes him feel as if you look up to him and gives the message that you want to be with him. You know for sure that he likes this if he rests his head on top of yours in return. Be careful, though, not to do this too much or while he is talking. Another way to lead into it can be to say something like "What would I do without you?" or "I love you." or while you are both smiling/laughing.