**Talk about current events - Things going on in your town and all over the world, tell him something you heard on the news etc, discuss your feelings about it, ask his.
**Talk about pets - if you have one, if you want one, ones you have had in the past, his pet... animals are interesting creatures !
**Talk about music, movies you've seen, your feelings about them ask his, etc.
**Talk about your hopes and dreams, your goals, where you see yourself and find out his hopes and dreams and where he see's himself.
**Talk about family, your's or his, memories, etc.
**Talk about food, what you ate, what you want to eat etc.
**Talk about each other's days, the best and worst parts of them
**Talk about naughty stuff , if you guys want to
**Share a joke, or funny quote
**Recite some lyrics that mean something to you, or him, or that are just awesome regaurdless
**Talk about travel, where you have been - where you want to go - same for him.
There is just infinite things to talk about, but you also have to learn to appreciate the silence two people that are close can share with no pressure.
To engage him in conversation... be sure to ask questions that can't be answered with a yes or no, if they are yes or no questions, have a follow up to it that can ease him into elaborating.
EX... Would you ever want to visit Paris?
That can be answered with a yes or a no, stopping the convo...
EX ...What do you think would be fun about visiting paris?
Requires a more elaborate response, even its just to say "Oh I don't think it would be fun"... that could help lead to a discussion on why he wouldn't like to... or where else he'd like to go and for you to talk about the same.
Once you get the ball rolling in one topic, its easy to transission on to another as more and more things pop into your head, same will happen to him - some funny memory, something read or seen on tv that is related .. etc.