I haven't been on the Ruby, but there will be an in cabin safe. There is no charge for this.
I'm just going to guess from experience, but the safe is not very big. It will hold your billfolds, cash, credit cards, cell phones, jewelry, and not much more. If you need a larger box, check with the Purser's office. There's no charge for using those boxes, either.
I always bring a grocery card or an expired credit card to use if the safe needs a card. If not, you can program the safe with any numbers or letters you choose.
As Kuki said, never use your onboard keycard. If you lose it and someone else finds it and gets into your room... !