We try to plan Family Home Evening in advance, but sometimes the most fun we have had has been when we've been the most spontaneous.
A couple of weeks ago we decided to play Scripture Spoons. We laid out 5 spoons, then played the regular Spoons card game, but left the Jokers in. Whenever a Joker was passed, someone would read a few verses from the scriptures. Then, when a player collected a hand with four-of-a-kind and grabbed spoons, whoever was left without a spoon read some more.
We played for quite a while, and will probably play every few weeks.