When planning an event for 100 guests, it's customary to prepare one favor per guest. This ensures that everyone attending your event receives a token of appreciation. However, it's always a good idea to have a few extra on hand, just in case there are last-minute additions to your guest list. So, for an event with 100 guests, you might want to consider ordering around 105-110 favors. This approach ensures that every attendee gets a favor and you won't run out if there are unexpected guests.