/item and /replaceitem Command Generator

A carved pumpkin on the nearest player’s head and 16 torches in the first slot of the chest below you:

Java 1.17 and later

item replace entity @p armor.head with minecraft:carved_pumpkin
item replace block ~ ~-1 ~ container.0 with minecraft:torch 16
item replace entity @p armor.head from entity @s weapon.mainhand
item modify entity @p weapon.mainhand my_pack:make_shiny

/item can also copy one slot into another and run an item modifier on a slot (make one with the item modifier generator). Item data goes right after the ID: components in square brackets from 1.20.5 ([unbreakable={}]), NBT in curly braces before. A slot holds up to 99 from 1.20.5, 64 before. Slots changed over time: horse.armor became armor.body in 1.20.5, horse.saddle became saddle in 1.21.5, and contents, player.cursor and player.crafting.0–3 arrived in 1.20.5.

Java 1.8 to 1.16

replaceitem entity @p armor.head minecraft:carved_pumpkin           (1.13 – 1.16)
replaceitem entity @p slot.armor.head minecraft:pumpkin 1             (1.8 – 1.12)

Before 1.13 slot names start with slot., the count is always written and NBT goes after a data value (1 0 {…}). Item names were different then too (carved pumpkins did not exist), so check the ID against your version. 1.8 calls the main hand slot.weapon and has no off hand.

Bedrock

replaceitem entity @p slot.armor.head 0 carved_pumpkin
replaceitem block ~ ~-1 ~ slot.container 0 torch 16
replaceitem entity @p slot.hotbar 0 keep diamond_sword 1 0 {"minecraft:item_lock":{"mode":"lock_in_slot"}}

Bedrock writes the slot type and number separately. keep only fills an empty slot. The JSON at the end can lock the item in its slot or inventory and keep it on death; Bedrock has no other item data in commands, and no copying or item modifiers. slot.armor.body (wolf and horse armour) needs 1.21.20; older versions use slot.armor, which only horses have. To hand an item over normally, use /give.