I have seen a few post’s asking about looting on missions so here goes 
It breaks into 2 type’s.
These are the missions where you Do Not Have To Loot you get all the contents of chests and what it dropped by enemy unit’s.
All Haven type missions.
Scavenging missions.
All Special missions (Does not matter if its a EVAC)
Nests.
These are the missions where you Do Have To Loot.
Lair Missions.
Citadel Missions.
Ambush Missions.
Quick Tip’s.
1: All Chest’s give’s the unit opening it 5 WP.
2: All Chest’s combined at a haven has a mix of ammo type’s and grenades with medi kits and 1 weapon or armour piece related to the faction map.
hope this helps