If you need some upgrades go to the previous levels you completed and beat your original scores and you get additional style points to spend on upgrades. I think the useful ones to get is

Body Armour ( Increases The Punisher's Damage )
Kill Recovery ( Enemy kills refills your health )
Longer Slaughter Mode ( Makes the blue bar longer )
Attach Grenade Launcher ( Assault Rifle grenades )
Attach Silencer ( Less Attention with weapons )
Attach Scope ( Useful for shooting down enemies )
Increase Grenade Capacity ( Increases grenade ammo to 10
Increase Ammo Capacity ( Fills up ammo quicker )
Increase Magazine Size ( Upgrades Magazine )
Increase Accuracy ( Increases the range )

You find out which you prefer but instead of throwing the grenades they are much better with the assault rifle's or battle rifle's grenade launcher.