I definitely second the smoked salmon and crackers. Smoked food, even small bites, are often a bit heavy and rich. But with smoked salmon you can still provide a smoked food, but it's a nice and light/refreshing option for people as well.
Here are some that I made a while back. Instead of just cream cheese I also whip in some creme fraiche, a little lemon juice, and some fresh dill. Everybody loves them.