Hi Anansis, this is probably a little bit late but I've just noticed this thread. I fly regularly with Air Asia and the amount of hand luggage they allow into the cabin is absurd. I've seen people in the boarding lounge with five separate pieces of luggage and I'm talking about luggage they obviously arrived at the airport with, not what they bought there.
Air Asia could make a killing if they enforced their own policies (a la Ryanair etc) but I find that employees (and people in general) in South-east Asia (particularly Indonesia where I live) prefer to turn a blind eye to the indiscretions of others rather than confront people about them.
Anyway, I'm sure you'll have no problems taking all your shopping on board!