When cruising overseas, we have bought the duty free alcohol for cruise friends that were doing B2Bs and have also been the recipient of such a favour.
We have also loaded extra credit onto the card if our expenses are likely to exceed the limit and / or we would still be away for the first months payment.
We haven't bought duty free alcohol aboard a ship for a long time but some other things maybe worth it, I am told (niece and friends) that some lines of make-up are priced nicely for savings.