[SDPhantom]

It can with a few tweaks. I added notes for educational purposes and fixed skipping free container slots if it encounters an empty inventory slot.

local InventorySlots={--    Comment or remove whichever slots you don't want to process, these enums exist in all clients
    INVSLOT_AMMO;
    INVSLOT_HEAD;
    INVSLOT_NECK;
    INVSLOT_SHOULDER;
    INVSLOT_BODY;
    INVSLOT_CHEST;
    INVSLOT_WAIST;
    INVSLOT_LEGS;
    INVSLOT_FEET;
    INVSLOT_WRIST;
    INVSLOT_HAND;
    INVSLOT_FINGER1;
    INVSLOT_FINGER2;
    INVSLOT_TRINKET1;
    INVSLOT_TRINKET2;
    INVSLOT_BACK;
    INVSLOT_MAINHAND;
    INVSLOT_OFFHAND;
    INVSLOT_RANGED;
    INVSLOT_TABARD;
};
 
local function UnequipAll()
    if #InventorySlots<=0 then return; end--    Sanity check
    local slotindex=1;
 
    ClearCursor();--    Make sure the cursor isn't holding anything, otherwise we might accidentally issue an item swap instead of an unequip
    for bag=NUM_BAG_SLOTS or NUM_TOTAL_EQUIPPED_BAG_SLOTS,0,-1 do-- CE and Wrath use NUM_BAG_SLOTS, DF uses NUM_TOTAL_EQUIPPED_BAG_SLOTS
        local free,type=(C_Container or _G).GetContainerNumFreeSlots(bag);--    C_Container is used in Wrath and DF, CE still has this in _G
        free=(type==0 and free or 0);-- Uses a quirk with this style of condition, only process bags with no item type restriction with fallback to zero if no bag is there (if free is nil, it'll fallback to zero even if the condition is true)
 
        for _=1,free do--   Variable is unused, we just need to loop for every free slot we see
            local invslot=InventorySlots[slotindex];--  Cache slot mapped to current index
            while not GetInventoryItemID("player",invslot) do-- Loop if no item in slot and until we find one
                if slotindex<#InventorySlots then slotindex=slotindex+1; else return; end-- Increment to next index or stop when we have no more inventory slots to process
                invslot=InventorySlots[slotindex];--    Update to new slot
            end
 
--          This pair is a complete operation, cursor is expected to be clear by the time both of these lines have run
            PickupInventoryItem(invslot);
            (bag==0 and PutItemInBackpack or PutItemInBag)((C_Container or _G).ContainerIDToInventoryID(bag));--    First set of parenthesis chooses function to run before calling it, PutItemInBackpack() doesn't accept any args, so ContainerIDToInventoryID() is safe to run regardless
 
            if slotindex<#InventorySlots then slotindex=slotindex+1; else return; end-- Increment to next index or stop when we have no more inventory slots to process
        end
    end
end