This oldy but goodie is one I did with Erik when he was little. He tended to think that if he was in his high chair I owed him some food, so we had to do a little improvisation, but Maren had no problem hanging out in there.
Set up is simple. Grab a few item from around the house, tie them to some string, and tape the string to your child's high chair tray. If they don't figure out what to do after a few minutes you can show them that there is something on the end of the string.
Once Maren realized there were interesting things at the end of the strings she was hooked. This kept her busy long enough for me to get a few boxes packed for our move. That means it's a win in my book!