I've had a 60 L backpack for almost seven years now. Nothing on it is broken and it fits my needs, so right now I don't have any thoughts about replacing it (Getting a light pack might be the only reason to do so).
However, I've started to think about what I will do if buckles, straps or zippers break. They've taken quite some abuse in the past; while I will do my best to prevent damage, I can't guarantee much. To prevent an unfortunate situation: What things should I be especially aware of and how - if possible - do I take care of such issues?