I will show how to do this in Remeres MapEditor.
Right click on the chest and select properties.
in the Action ID wright 2000
in the Unique ID wright a storage number that you don't use for a quest, script or something else.
A example: on my we use a system like this, all quest chest got Unique ID 20000+ so:
Quest number one: Unique = 20001
Quest number two: Unique = 20002
and so on
pic: XXXX = the storage numbaer
After that you can use the contents to add all the items you want the player to get in the quest. something like this:
You can add one item or a lot of items or container with items but it's a really nice system and it's easy to use if you know how it works
Credits to:
JoccE (For making the guide)
TFS Team (For the system)