By gut feel, I'd go with "was" as well, but not because of the timing : after all, you wouldn't say "A cashbox and a necklace
was stolen", even if they were stolen all at once.
I think it's probably because:
A cashbox is a
thing (singular);
a necklace is a
thing (singular); together they are two
things (plural).
Whereas:
Money
is "
stuff" (singular); jewellery
is "stuff" (singular); together they make more "stuff" (still singular).
I've deliberately avoided grammatical terms here, because I'm not sure my gut-feel is grammatically justifiable.
Any grammarians care to agree or disagree?
W
