SAPCOR1
Journeyman Pro
A friend of mine was told at East Midlands (one of the worlds' worst) airport that he couldn't take them in his hand baggage so had to hand them in.
Anybody else think maybe the reason the OP is asking about handluggage is that they're flying cheap and not-so-cheerful, so no check-in luggage?
The obvious answer to anybody is to put them in the hold but if you're not already checking anything in, it's expensive just for golf balls and probably better off buying them there!
(I could be lying to you here but) I think I took a dozen in my handluggage last year without issue.