Bukkit

As stated by the main page, each world has its own generated dungeons, pyramids, and starter chests. With these come configurable items. To define each item put "<material id>:<stack size>" or "<material name>:<stack size>". Some examples:

properties:
    pyramid-items: 'APPLE:3 SAPLING:5'
    dungeon-items: '1:3 5:3'
biomes:
    Taiga:
        starter-items: 'SAND:64'
    Jungle:
        starter-items: 'SAND:64'
    Forest:
        starter-items: 'SAND:64'
    Plains:
        starter-items: 'SAND:64'
    Desert:
        starter-items: 'SAND:64'

With the "starter-items", the items are simply put into the chest. The pyramids and dungeons however read in the info differently. They first select a random number of times to cycle though. Each time it cycles through it:

• First selects a random item from the list you provide
• Selects a random stack size ranging from 1 to the stack size defined
• Selects a random index in the chest, ignoring whether or not the index is empty
• Puts the item at that index