luggage – Can I use plastic bag as a personal item

I am allowed to bring 1 carry-on luggage up to 7 kg and 1 personal item up to 5 kg. My carry-on luggage (backpack) will weight around 8 kg, which seems to violate the limit. Can I take 1 plastic bag (within size limits of personal item) and take some stuff from backpack to the plastic bag, so that now my 8 kg will be distributed as 6 kg carry-on and 2 kg personal item?

If content matters, assume that the plastic bag contains a laptop.