If you drop in to Kempegowda Bus Stand (Majestic) on 15th and 16th, you might be able to get a bus to your destination without reservation. On the other hand, if you decide to reserve your tickets, you will be saving some money too.
Many special KSRTC buses from across Bangalore, with advance booking facility, will help you out! Travel with four people and get 5% discount on the fare, get 10% discount for booking return ticket!