Veteran mode - Reach Level 32 to unlock Veteran mode, which is a Co-op mode with much tougher enemies.

Bonus weapons - Successfully complete the indicated task to unlock the corresponding weapon or weapon attachment:

Bolt Action Rifles

Springfield: Reach Level 4.
Bayonet: Successfully complete Marksman Challenge 1 (increases melee attack range).
Rifle Grenade: Successfully complete Marksman Challenge 2 (grenade launcher attachment, replaces Perk 1 slot).
Arisaka: Reach Level 4.
Sniper Scope: Successfully complete Marksman Challenge 1 (increases accuracy and range).
Bayonet: Successfully complete Marksman Challenge 2 (increases melee attack range).
Rifle Grenade: Successfully complete Marksman Challenge 3 (grenade launcher attachment, replaces Perk 1 slot).
Mosin-Nagant: Reach Level 21.
Kar98k: Reach Level 41.
PTRS-41: Reach Level 57.

Rifles

SVT-40: Reach Level 4.
Flash Hider: Successfully complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Aperture Sight: Successfully complete Marksman Challenge 2 (precision sight).
Telescopic Sight: Successfully complete Marksman Challenge 3 (enhanced telescopic sight).
Gewehr 43: Reach Level 7.
Suppressor: Successfully complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Aperture Sight: Successfully complete Marksman Challenge 2 (precision sight).
Telescopic Sight: Successfully complete Marksman Challenge 3 (enhanced telescopic sight).
Rifle Grenade: Successfully complete Marksman Challenge 4 (grenade launcher attachment, replaces Perk 1 slot).
M1 Garand: Reach Level 17.
STG-44: Reach Level 37.
M1A1 Carbine Reach Level 65.

Sub Machine Guns

Thompson: Reach Level 4.
Suppressor: Successfully complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Aperture Sight: Successfully complete Marksman Challenge 2 (precision sight).
Round Drum: Successfully complete Marksman Challenge 3 (increased ammunition capacity).
MP40: Reach Level 10
Suppressor: Successfully complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Aperture Sight: Successfully complete Marksman Challenge 2 (precision sight).
Dual Magazine: Successfully complete Marksman Challenge 3 (increased ammunition capacity).
Type 100: Reach Level 25.
Ppsh: Reach Level 41.

Machine Guns

Type 99: Reach Level 4.
Bipod: Successfully complete Marksman Challenge 1 (reduces motion for more accuracy).
Bayonet: Successfully complete Marksman Challenge 2 (increases melee attack range).
BAR: Reach Level 4.
Bipod: Successfully complete Marksman Challenge 1 (reduces motion for more accuracy).
DP-28: Reach Level 13.
MG 42: Reach Level 33.
FG 42: Reach Level 45.
Browning M1919: Reach Level 61.

Pistols

Colt M1911: Reach Level 4.
Nambu: Reach Level 4.
Walther P38: Reach Level 4.
Tokrev TT-33: Reach Level 21.
.357 Magnum: Reach Level 49.

Primary Grenades

Frag: Reach Level 4.
N 74 ST: Reach Level 4.
Molotov Cocktail: Reach Level 10.

Shotguns

M1897 Trench Gun: Reach Level 4.
Grip: Successfully complete Marksman Challenge 1 (vertical foregrip to reduce recoil, replaces Perk slot 1).
Bayonet: Successfully complete Marksman Challenge 2 (increases melee attack range).
Double Barreled Shotgun: Reach Level 29.

Special Grenades

Smoke: Reach Level 4.
Tabun Gas: Reach Level 4.
Signal Flare: Reach Level 4.

Extra custom weapon slots - Reach the indicated Prestige rank to unlock the corresponding extra custom weapon slot:

6: First Prestige
7: Second Prestige
8: Fourth Prestige
9: Seventh Prestige
10: Tenth Prestige

Perks - Successfully complete the indicated task to unlock the corresponding perk:

Perk Slot 1

Special Grenade x3: Reach Level 4 (three special grenades, no smoke).
Satchel Charge x2: Reach Level 4 (two remote detonation explosives).
M9A1 Bazooka x2: Reach Level 4 (bazooka with two rockets).
Bomb Squad: Reach Level 16.
Bouncing Betty x2: Reach Level 24.
Bandolier: Reach Level 40.
Primary Grenade x2: Reach Level 44.
M2 Flamethrower: Reach Level 65.

Perk Slot 2

Stopping Power: Reach Level 4 (increased bullet damage).
Fireworks: Reach Level 4 (higher explosive weapon damage).
Flak Jacket: Reach Level 4 (reduce explosive damage).
Gas Mask: Reach Level 4 (protect against Tabun Gas).
Juggernaut: Reach Level 4 (increased health).
Camouflage: Reach Level 12.
Sleight Of Hand: Reach Level 28.
Shades: Reach Level 32.
Double Tap: Reach Level 36.
Overkill: Reach Level 56.

Perk Slot 3

Deep Impact: Reach Level 4 (deeper bullet penetration).
Extreme Conditioning: Reach Level 4 (sprint for longer distances).
Steady Aim: Reach Level 4 (increased hip fire accuracy).
Toss back: Reach Level 6 (reset fuse of picked up grenades).
Second Chance: Reach Level 9 (revive downed allies).
Martyrdom: Reach Level 20.
Fireproof: Reach Level 48.
Dead Silence: Reach Level 52.
Iron Lungs: Reach Level 60.
Reconnaissance: Reach Level 64.

Vehicle Perks

Water Cooler: Reach Level 4 (decreased turret overheat).
Greased Bearings: Reach Level 4 (increased turret rotation speed).
Ordnance Training: Reach Level 12.
Lead Foot: Reach Level 28.
Coaxial Machine Gun: Reach Level 40.