The wine packages are basically a convenience if you plan to purchase multiple bottles of wine over the course of the cruise. The various choices are a three-bottle, four-bottle, seven-bottle packages. Longer cruises may have even larger packages available. Their are two tiers, one more basic choices and the second more premium. You select your bottles from whichever package you have purchased. There is typically a small savings over purchasing the same bottles al a carte, but your choices are also more restricted in that there are additional bottles of wine available from the al a carte wine list. Whether you purchase a package or purchase individual bottles al a carte or purchase individual wines by the glass is really a matter of taste. I've used all three approaches on different cruises and been generally happiest with purchasing al a carte bottles or wines by the glass to pair with particular meal choices. This has provided access to a broader selection than the wines on either the standard or premium packages. The one time I purchased the premium package in anticipation of having a decent French red to drink at Remy, I discovered that I could not use the wine package there. So I ended up ordering wines by the glass even there.
Because DW does not drink alcohol while cruising (and seldom drinks much even at home), I can usually stretch a single bottle of wine over two dinners. The servers (actually your assistant server handles most beverage service) will store an unfinished bottle and bring it to the dining room the following day. Alternately, you can take an unfinished bottle back to your stateroom to finish it there. The last two cruises, I have purchased a bottle at Palo and then finished it in the MDR the following evening.
For wines by the glass, the executive chef and sommelier include some food pairing recommendations on the dinner menus in the MDRs. Sometimes I try these to experience a new wine when I would not want to purchase a full bottle just for myself. Some of these pairings have been quite good.
