  <tag:items:crafttweaker:leather_material>.add(<item:minecraft:leather>,<item:minecraft:rabbit_hide>);
craftingTable.addShaped("backpacked_backpack_leather", <item:backpacked:backpack>, [[<tag:items:crafttweaker:leather_material>, <tag:items:crafttweaker:leather_material>, <tag:items:crafttweaker:leather_material>], [<tag:items:forge:string>, <tag:items:forge:ingots/iron>, <tag:items:forge:string>], [<tag:items:crafttweaker:leather_material>, <tag:items:crafttweaker:leather_material>, <tag:items:crafttweaker:leather_material>]]);

craftingTable.removeByName("backpacked:backpack");