To configure object spawn inside the chests, you can edit to pokestop.json config file.
{
"respawnLootTimer": 600,
"lootTable":
[
[
{
"item": "minecraft:clay",
"min": 10,
"max": 10,
"meta": 0,
"chance": 50
},
{
"item": "minecraft:clay_ball",
"min": 1,
"max": 10,
"meta": 0
}
],
[
{
"item": "minecraft:dirt",
"min": 5,
"max": 10,
"meta": 0,
"chance": 30
}
]
],
"lootTable2":
[
[
{
"item": "minecraft:clay",
"min": 10,
"max": 10,
"meta": 0
},
{
"item": "minecraft:clay_ball",
"min": 1,
"max": 10,
"meta": 0,
"chance": 80
}
],
[
{
"item": "minecraft:dirt",
"min": 5,
"max": 10,
"meta": 0
}
]
]
}
respawnLootTimer defines how many ticks have to pass until new loot is generated.
lootTable defines a List of Lists containing ItemStacks you want to spawn, you can also define the amount and meta.