Tapes/Heralds/Id Cards (Minimal Information Given)
Spoiler:
--Act 1
---Resort- Tapes 1&2 Heralds 1-12 Id Cards 1-25
----Parking Lot- Tapes 3 Heralds 13-16 Id Cards 26-30
--Act 2
---Church- Tapes 4&5 Heralds 17-23 Id Cards 31-45&58-60
----Sewers- Heralds 24 Id Cards 46-49
-----City Hall- Id Cards 50-52
-----Market- Heralds 25-27 Id Cards 53&54
-----Police Station- Tapes 6 Heralds 28&29 Id Cards 55-57
--Act 3
---Jungle- Tapes 7 Heralds 30-32 Id Cards 61-73
----Labratory- Tapes 8&9 Heralds 33-37&40 Id Cards 74-85
--Act 4
---Prison- Tapes 10 Heralds 39 Id Cards 86-92&94-99
----Hospital- Tapes 11&12 Heralds 38 Id Cards 93&100
The information below is from g4tv and has been edited to only show complete quest items
Spoiler:
----Blade
Sickle - Complete "Life In The Bag" Side Mission Location: Resort
Wicked Sickle - Complete "Six Feet Under" Side Mission Location: City of Moresby
Military Machete - Complete "Night Hawk" Side Mission Location: Resort, When you reach the Jungle
Homemade Machete - Complete "Family Matters" Side Mission Location: Resort
Bolo Machete - Complete "Faith Will Move Mountains" Main Mission Location: City of Moresby
Hatchet - Complere "Blood In The Tropics" Side Mission Location: Jungle
Big Splitting Axe - Complete "Radio Ga Ga" Side Mission Location: City of Moresby
Homemade Cleaver - Complete "Exodus" Main Mission Location: Resort
Wakizashi - Complete "Message of Love" Side Mission Location: Laboratory
Double Blade - Complete "Bloody Valentine Side Mission Location: Resort
Homemade Double Blade - Complete "Bloody Valentine" Side Mission Location: Resort
Battle Double Blade - Complete "Danse Macabre" Side Mission Location: Laboratory
Reaper - Complete "Man Of Faith" Main Mission Location: Laboratory
Kukri - Complete "The Dead Don't Eat Crackers" Side Mission Location: Laboratory
Slicer - Complete "My Precious" Side Mission Location: Resort
The Machete - Complete "Where Is My Pineapple?" Side Mission Location: Laboratory
----Guns
Pistol - Complete "The Second Head Of Cerberus" Side Mission Location: City of Moresby
Heavy Pistol - Complete "In Cold Blood" Side Mission Location: City of Moresby
Revolver - Complete "Omar Escort" Side Mission Location: Resort
Magnum - Complete "Rotting Flesh" Side Mission Location: Laboratory
Auto Rifle - Complete "Chasing Shadows" Main Mission Location: Jungle or Police Station
Short Shotgun - Complete "Wet Job" Side Mission Location: Laboratory
----Bombs
Molotov - Complete "Ashes To Ashes" Side Mission Location: Resort
----Weapon Mods
Deo-Bomb - Complete "Tell Me Where It Hurts" Side Mission Location: Resort
Deathstalker Mod - Complete "Subtance of Matter" Side Mission Location: Laboratory
Nuts & Bolts Mod - Complete "Toy Story" Side Mission Location: Resort
Detox Gun Mod - Complete "Insect Repellent" Side Mission Location: Laboratory
Detox Shotgun Mod - Location: Bungalow 3 In Laboratory during "Where Is My Pineapple" Side Mission
Torch Mod - Complete "Counsel of Despair" Side Mission Location: Resort
Nail'd Mod - Complete "Passport To Life" Main Mission Location: Resort
Heavy Mod - Complete "Two Hearts" Side Mission Location: Resort
Shock Mod - Complete "Black Hawk Down" Main Mission Location: Resort
Old Smoky Mod - Complete "Spy Game" Side Mission Location: Abandoned House in City of Moresby
Sticky Bomb Mod - Complete "Drowned Hope" Main Mission Location: City of Moresby
Impact Mod - Complete "Last Chance On The Wall" Side Mission Location: City of Moresby
Striker Shotgun Mod - Complete "A Wounded Crank" Side Mission Location: Jungle
Shock Rifle Mod - Complete "Power Slaves" Side Mission Location: Laboratory
Shark Mod - Complete "Death Wish" Side Mission Location: Jungle
Short-Circuit Mod - Complete "Judgement Day" Side Mission Location: City of Moresby
Paralyzing Strike Mod - Complete "Picture of Bliss" Side Mission Location: City of Moresby
Piranha Mod - Complete "The Third Head of Cerberus" Side Mission Location: City of Moresby
Pride Gun Mod - Complete "Matter of Justice" Side Mission Location: City of Moresby
Magic Wand Mod - Location: City Hall Part 2, In The Center of City Hall
Pride Shotgun Mod - Location: Police Station, In the security room.
Tesla Mode - Location: Laboratory Inside the Warehouse
Below is the link to a forum post that contains found skulls and skull drop-off points with their respected dev mods
Spoiler:forums.steampowered.com/forums/showpost.php?p=24950149&postcount=1
Lastly, Off-topicish but good information about the impact of multiplayer as well as level scaling
Spoiler:
__________________________________
|_Players_|_Enemy Hp_|_Enemy Damage_|
|____2___|____1.25___|______1.1______|
|____3___|____1.75___|______1.2______|
|____4___|____2.25___|______1.3______|
_________________
|_Level_|_Walker Hp_|
|___1__|_____100__|
|___3__|_____300__|
|___12_|_____620__|
|___20_|____1100__|
|___25_|____1600__|
|___50_|____4000__|
And yes...I do so enjoy the way my tables look...