Summary
Soldiers will drop items when using the "Spit it out" interrogation in the field, somewhat similar to the MGS4 "frisking" feature.
Requires Infinite Heaven!

How to enable
1. Open the Infinite Heaven menu in-game
2. Open the Interrogation menu
3. Switch "Enable interrogation item drops" to ON

How to use
1. Hold up a soldier in-game
2. Select the "Spit it out" interrogation option
3. If the soldier does not provide any special information, they will drop an item
4. The command can be used until the soldier runs out of items

A soldier will drop a limited amount of items; enable the "Show announce logs" option in the menu to see the drop count log
in-game. Have fun!