Food outlets in HKG do not take foreign cash the last time I checked. Some shops may but I'll really doubt it'll be the shops that sell snacks (maybe those that sell duty free).

Your friend doesn't even have a UK/NZ debit Visa/MC card? Mind you, even if they do, not all food outlets take them.

But there's enough Travelex points throughout HKG restricted area http://www.hongkongairport.com/eng/s...oney/trav.html . Your friend just has to know where they are and not care about the rate too much.