We are off on our 30th cruise next week on P&O (not all cruises with P&O!). We have never had a drinks package of any sort, 'cos when you work it out, you have to be drinking about a dozen drinks a day to make it worthwhile. Haven't been on P&O for a couple of years, but normally their prices are roughly pub prices eg £4 - £5 for a beer or spirit + mixer (I realise you are non alcoholic, but just trying to give you an idea). If you go on Royal Caribbean or Celebrity, their prices are higher (around $7 -$8 for same) and their packages are more expensive, so as I say, we never have a drinks package.
As this is your first cruise, another piece of advice...DO NOT buy a wifi/internet package! You will be paying every day for what you can get for nearly all year at home. Most cruise terminals have free wifi (just follow the crew!) and the internet on board is normally really slow and cr@p anyway.
Have fun!
PS Are you going on Ventura?...we are.