The following was gleaned from PUBYAC contributors. If you're a member check out the archives for July 2010. Your colleagues appreciate hearing what works and what doesn't work for you.

Have music playing when the patrons are arriving.  It's great if something "fits" with the program, but sometimes it works by just grabbing a CD that looks interesting. 

Have coloring sheets, word searches, or crosswords that relate to your topic. The participants might be inspired to work together solving the puzzles. Another possibility is to give them a long strip of paper on a wall or table and some markers and just let them write or draw. They can doodle, play games (like Hangman), draw mazes and such.  The kids often strike up conversations while drawing so it works as an ice breaker as well as time filler. For younger kids, they can just doodle, or draw something that has to do with the topic of the event. OR you can start a picture and have them put themselves in it or add elements that are missing.

Icebreakers are great for mingling, team-building, or just filling time, plus, if you consistently do a fun activity, people may not want to miss anything, and will try to get there on time.

TEENS--

Teens may not always know how to break the ice with other teens, but they do know how to help.  Leave a couple of things undone for the first teens that show up - let them put out the chairs, pass out any books, handouts, etc.  Ask one of them to check incoming teens off the roster.  Once the teens are actively involved in the process, a lot of their awkwardness fades away.

Ask for input on future teen activities, either have a list and have attendees check which ones they want to attend or just ask for ideas and let them go at it. 

A fun "get to know you" activity where everyone can participate while waiting for things to get officially underway is sort of like bingo but with people.  Each gets a chart with various things written in each square like "has their own blog", "likes to play video games", etc.  Then the individuals go around the room and try to find someone who fits one of the items on the paper.  This could be a good way for the teens to get talking to one another and find out a little bit about the other people which is great if you are planning on doing a series of programs.

A classic that comes to mind is the "who/what am I?" game.  You write a name or object on an index card, and have the participants hold or tape it to their forehead, facing out so that others can read it.  Each person has to figure out what their card says by asking yes or no questions of the others.  It's a good way to get people talking.  Obviously the words have to be pretty common knowledge, but you could probably do themes, like book characters or something.  Setup and explanation and materials are all minimal, and it's the kind of thing teens can have fun with.

Place little things around the room for the participants to look at, related to whatever the program is about, or have some trivia question cards sitting around on the tables.

An I spy activity can work well and they can do it in groups to get to know each other. Get baby food jars and put bird seed and some small objects.  Provide a sheet with some questions on it (eg. What color are the buttons in the jar, how many paper clips), that keeps them occupied.  You can make up as many jars as you like depending on the size of the group.

With the teens I always have food out. Just like adults, when you can fill a plate and stand their munching, you at least have something to do with your hands and mouth rather than standing around feeling at loose ends!