[Kanegasi]

classic has the item api retail uses, at least according to the code extract. Here's what I use in a retail weakaura to track and loot openable looted items:

if event=="BAG_UPDATE_DELAYED" then
    if not aura_env.combat and not InCombatLockdown() then
        for b=BACKPACK_CONTAINER,NUM_BAG_SLOTS do
            for s=1,GetContainerNumSlots(b) do
                if GetContainerItemID(b,s)==45724 then
                    aura_env[(Item:CreateFromBagAndSlot(b,s):GetItemGUID())]=1
                    UseContainerItem(b,s)
                end
            end
        end
    end
elseif event=="LOOT_OPENED" then
    for i=GetNumLootItems(),1,-1 do
        if aura_env[(GetLootSourceInfo(i))] then
            LootSlot(i)
        end
    end
end

The bag update event opens the specific openable I'm tracking while saving that bag's GUID, then the loot opened event checks the loot source and if it's a guid I saved, autoloot it all.