minecraft-pack/kubejs/data/merrymaking/loot_modifiers/present_in_ship.json

{
  "type": "merrymaking:add_item",
  "conditions": [
    {
      "condition": "neoforge:loot_table_id",
      "loot_table_id": "minecraft:chests/shipwreck_supply"
    },
    {
      "chance": 0.05,
      "condition": "minecraft:random_chance"
    }
  ],
  "item": "merrymaking:present"
}