Get/Use Railgun & Stungun in Freemode + Refill your Fireworklauncher Ammo!!! Destroy the crates in front of you and you will get full ammo of the weapon that drops out. Use a car for BEST results!
Make sure to select owned weapons on job-start screen. Pick up the weapons, then quit through the phone. You will keep the Railgun and Stungun until you die or switch lobbies!