On the very first level of the game, take Rolo and go to the man who holds the keys to the cages. Leap onto his head and rescue the rabbit in the cage. Press START and then transfer control to the rabbit. Hop left, to the beginning of the level and jump straight up to collect the 1-Up. Press START and go to the map. Go into the same level that you were just in and do the same process over and over again to collect as many 1-Up's as you like.