How much Hong Kong dollars and RMB can I bring across the border from the Mainland to Hong Kong?

No more than 20,000 RMB or 5,000 USD (or equivalent foreign currency).

If you exceed it, and you don't have declare in advance, your excess will be confiscated according to the regulations, and you will be fined. But the general customs will not check your cash unless your package is too big or you look nervous and have been sampled (unlucky). However, it is generally not recommended that you bring too much cash. On the one hand, it is illegal and not worth being confiscated. On the other hand, it is easy to be stolen and has a great loss.

It is best to bring a foreign exchange credit card or a RMB credit card with UnionPay function to Hong Kong (most shops in Hong Kong accept RMB UnionPay cards), which is the best and most convenient. If you have to bring cash, I think it's enough to include accommodation, travel, transportation and catering. It's 65438 Hong Kong dollars +0000-2000 per day.