Apart from small bits and bobs we find it easier to buy all the chocs and little bits for the kids there as it lightens the luggage and choclate left in a suitcase in the heat of phill and possibly your transit airport won't be too good.
At Naia there is a diddy one by the waiting area but it is worth if you have your own transport poping round the corner and stocking up. As im told by the mrs things are slighty cheaper and older realtives mucho grateful for the 12 packs of corned beef, spam and coffe etc.
The bigger store takes a good couple of hours to get round if you go round with a big group.
Also you can go on a later day if its more suitable.
I also noticed apart from ensuring everything was paid for no one seemed to care how much you actually bought well within reason.