In levels 2-1, 2-2, and 2-3, you can get a machine gun and/or machine gun ammo clip from every heli you destroy. Get the heli down to enough health, so that it will only require one grenade to kill it. Use Hyper Jump (hold [Modify] and press [Jump]) to get very close to the heli. You must be close enough to touch it. Use a grenade to finish it off. The heli will drop a machine gun clip with only 25 ammo in it. Note: This will not effect any of the weapons that the helis usually drop; every other time you use this trick you will get two items.