If 「お金は」 weren't in there, then yes, を (or the contrastive は) would be more appropriate.
Since it is in there, you can think of this as saying it's best not to carry money "in the form of" or "by means of" cash (with the nuance, of course, being that you should instead bring a payment method in the form of credit cards, traveler's checks, etc.)
Ah, it is so clear now, thanks to your explanation. お金は could be thought of as the object of 持って行く that has become topicalized. Thus, your translation is perfect: "best not to carry money in the form of cash".
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.