Default items are below, add your own via NBT, here's an example:
{id:"minecraft:elytra", Count:1, components:{ "minecraft:enchantments":{levels: {"minecraft:unbreaking": 10}}, "minecraft:custom_name": '"General Kenobi"'} }
{id:"minecraft:command_block", Count:1}
{id:"minecraft:chain_command_block", Count:1}
{id:"minecraft:repeating_command_block", Count:1}
{id:"minecraft:spawner", Count:1}
{id:"minecraft:jigsaw", Count:1}
{id:"minecraft:structure_block", Count:1}
{id:"minecraft:structure_void", Count:1}
{id:"minecraft:barrier", Count:1}
{id:"minecraft:dragon_egg", Count:1}
{id:"minecraft:debug_stick", Count:1}
{id:"minecraft:knowledge_book", Count:1}
{id:"minecraft:command_block_minecart", Count:1}
{id:"minecraft:light", Count:1}
{id:"minecraft:bundle", Count:1}
