Mak: My wife and I cruised the Triumph (Western Caribbean) in April. I took $1,300 US Cash (we are from Canada) and did not bring much of it home. Although we secured our Sign and Sail cards with a credit card, we paid if off with cash to avoid the "after effects" of credit. Our S &S bill was about $650.00 (our tips were prepaid), of that, about 400.00 was bar tab (wine with dinner, etc), 250 was one excursion for 2 (river tubing in Jamaica-great fun) and some items from the duty free store. The balance was shopping in various ports, probably blew $350.00 dollars in the casino--rest was extra tips in ports, some duty free liquour in Cozumel, drinks at "Fat Tuesdays" that sort of thing. So, I would say $1000 plus access to a credit card would be plenty.
We had a great time and don't regret spending any of the money (well, the Casino didn't seem to pay off bigtime for anybody, so you could avoid it and save some money--but the flashing lights and chiming machines are pretty attractive).
Hope this helps.