The secure Kappa container in Escape from Tarkov is the end game secure container that can be obtained after finishing Fence’s quest Collector. See below for the items you are required to find.
The requirements to unlock Collector quest according to the Wiki are the following:
Complete ALL Quests except:
Regulated materials, No offence, Trust regain, Loyalty buyout, Hippocratic Vow, Mentor, The stylish one and An apple a day – keeps the doctor away.
Related: How To Get The Gamma Container
What Can The Kappa Container Contain?
Small S I C C case
Weapon mods (Besides special scopes and some mounts)
Keys & Maps
Fence's Quest 'Collector' Objectives
To get the Kappa secure container you need to collect the following items IN RAID.