Which difficulty is best for collecting KF2 items?

Normal. Collectible achievements are not tied to any difficulty, and lower difficulty means slower, less aggressive Zeds and more time between waves.

Which perk should I use?

Berserker. It resists being grabbed so Zeds do not stun you while you move, and its night vision helps in dark rooms.

How long should the match be?

Set the game length to 10 waves so the match does not end before you finish collecting.

Collectibles & Achievements

KF2 Collectibles Guide: All Map Items With Video Routes

Each official Killing Floor 2 map hides a set of collectible items, and gathering them all unlocks that map's collectible achievement. This guide pairs a short routine with one video per map. The author's videos are recorded in a single take with no cuts, so you can see how every item location connects to the next and never have to search a level pixel by pixel. No video exceeds 5 minutes. For the wider achievement list see KF2 achievements.

Why this guide

Items are collected in one continuous take, so the path between spots is always shown.
No disorientation, forgotten items or false routes.
Every video is under 5 minutes.

How to do it

Difficulty. Pick Normal. The collectible achievements do not depend on difficulty, while higher levels make Zeds faster, quicker to grab and anger you, and shorten the trader time between waves. Set the length to 10 waves so the game does not end early.
Perk. Use Berserker: it cannot be pulled around by grabs (Zeds do not stun and turn you while you move), and it has night vision that makes items in dark areas easier to find.
In the match. Kill almost the entire wave, leaving the calmest Zed alive (a Bloat or a Cyst; the Cyst is the slowest). Then open the video for the map, check the item position, return to the game and collect. Watch your health and heal when needed; do not underestimate the enemy.

Maps, achievements and videos

#	Map	Achievement	Video
1	Biotics Lab	Biotics Bling	Watch
2	Paris	Paris Plunder	Watch
3	Volter Manor	Manor Money	Watch
4	Outpost	Outpost Offerings	Watch
5	Catacombs	Catacombs Cash	Watch
6	Evacuation Point	Point Paper	Watch
7	Black Forest	Black Forest Babies	Watch
8	Farmhouse	Darkness Dolls	Watch
9	Prison	Perilous Prison	Watch
10	Hostile Grounds	You've Got Red on You	Watch
11	Containment Station	Can't Be Contained	Watch
12	Infernal Realms	Infernal Relics	Watch
13	Zed Landing	ALAN!!!!!!	Watch
14	Nuked	Davy Crockett	Watch
15	The Descent	Hans Off the Merchandise	Watch
16	The Tragic Kingdom	The Wonderful World of Merchandising	Watch
17	Nightmare	Letting the Demons Out	Watch
18	Krampus Lair	A World Under Glass	Watch
19	Power Core	Surge Breaker	Watch
20	DieSector	It's aD.A.R.able	Watch
21	Airship	Powered by Steam	Watch
22	Lockdown	Shocking Discovery!	Watch
23	Monster Ball	Spooky Scary Skeletons	Watch
24	Santa's Workshop	Yule Shoot Your Eye Out	Watch
25	Shopping Spree	A Special Deal	Watch
26	Spillway	Money Down the Drain	Watch
27	Steam Fortress	All This Science I Don't Understand	Watch
28	Ashwood Asylum	Money Mania	Watch
29	Sanitarium	Oleaginous Old Ones	Watch
30	Biolapse	Nobel Prize for Destruction	Watch
31	Desolation	You are my Only Hope	Watch
32	Hellmark Station	Old Skull	Watch
33	Dystopia 2029	Like Tears in Rain	Watch
34	Moonbase	The Dark Side of the Moon	Watch
35	Netherhold	Forgotten Knowledge	Watch
36	Carillon Hamlet	Hidden Globes	Watch
37	Rig	Marine Research	Watch
38	Barmwich Town	Not Night Lamps	Watch
39	Crash	Lost Goods	Watch
40	Subduction	Projections from the Deep	Watch
41	Castle Volter	Cult of Personality	Watch

Second video set (another author)

A second Steam guide by a different author (https://steamcommunity.com/sharedfiles/filedetails/?id=2657747664) offers another full set of single-take videos, also recorded on the shortest game on Normal difficulty. The author reduces the first wave to a single slow Zed (a Bloat is best: it is the slowest early Zed and cannot grab you), says the class hardly matters (most items were collected as a Commando), notes the videos have no cuts except DieSector (the upper floor opens only from wave 8) and the maps whose waves move to a new floor, and says the guide grows with each new map.

#	Map	Video
1	Zedlanding	Watch
2	Dystopia 2029	Watch
3	Biolapse	Watch
4	Moonbase	Watch
5	Lockdown	Watch
6	Desolation	Watch
7	Airship	Watch
8	Hellmark Station	Watch
9	Sanitarium	Watch
10	Netherhold	Watch
11	Biotics lab	Watch
12	Paris	Watch
13	The Descent	Watch
14	Black Forest	Watch
15	Nightmare	Watch
16	Power Core	Watch
17	Monster Ball	Watch
18	Outpost	Watch
19	Nuken	Watch
20	Farmhouse	Watch
21	Catacombs	Watch
22	Containment Station	Watch
23	Evacuation Point	Watch
24	Volter Manor	Watch
25	Prison	Watch
26	Santa's Workshop	Watch
27	Hostile Grounds	Watch
28	Spillway	Watch
29	Ashwood Asylum	Watch
30	Shopping Spree	Watch
31	Steam Fortress	Watch
32	The Tragic Kingdom	Watch
33	Krampus Lair	Watch
34	DieSector	Watch
35	Infernal Realms	Watch
36	Carillon Hamlet	Watch
37	Barmwich Town	Watch
38	Crash	Watch
39	Rig	Watch
40	Subduction	Watch
41	Castle Volter	Watch

FAQ

Which difficulty is best for collecting KF2 items?: Normal. Collectible achievements are not tied to any difficulty, and lower difficulty means slower, less aggressive Zeds and more time between waves.
Which perk should I use?: Berserker. It resists being grabbed so Zeds do not stun you while you move, and its night vision helps in dark rooms.
How long should the match be?: Set the game length to 10 waves so the match does not end before you finish collecting.