We pack pretty much the same clothes for WDW as for the cruise though it might depend on the time of year for you. Other than formal and semi-formal nights if your cruise is long enough to have them and Palo's (and Remy's) if you intend to go, it's cruise casual or less all day. For me that means casual pants/khakis, shorts for the daytime, and a bunch of comfortable tops ranging from the very casual to slightly dressier and one fleece (it can be very cold on deck after dark and I find the theatres very cold).
We definitely do a park the day before the cruise but don't let it be a really late night. If you take the
DCL bus (we always do), then they pick up luggage at 8 am (I'm assuming you're staying on the grounds?) so you need to be up before then. Since the busses leave anywhere between 10:30-12:30 we always make sure to have breakfast no later than about 8 am (you don't need to be there for luggage pickup). Thus we don't want to be out too late the night before so that we are able to dress and finish packing well before eight without feeling cranky.
Whether it's worth it to you to take the DCL bus or drive is a personal decision. When I'm on a Disney vacation, I park my brains at the airport when I arrive. My day job is all about logistics and making arrangements, facility management, project management and tons of details. When I'm on vacation, I want someone else to handle it all for me. It may or may not be less expensive to drive yourself but I personally have no interest in picking up car, driving to port in an area unknown to me, dropping off family, dropping off car, taking shuttle. Blah. I prefer to just follow the person wearing the Disney name badge and do what they tell me.
We never bother to bring our own alcohol on board. As far as I am concerned, the cost of a few glasses of wine or other drinks is minimal in comparison to the rest of the trip and is no more expensive than buying it in any restaurant at home. It also gives me a full range of choices of different wines for dinner. Since my brain has been left at the airport, I just order the wine by the glass that's been recommended to be paired with the entree at dinner. I figure someone more knowlegeable than me has chosen it so why make a decision I don't have to. That gives me the ability to have a different wine with every meal. No brains required. As others have pointed out, all of the resort stores carry some range of wine and spirits and there are wines sold at the French, Italian and German pavillions at Epcot and I think at the kitchen store in DTD. More expensive than buying off-site but if you don't have a car, the cost of taking a taxi or renting a car would seem to me to wipe out the cost benefits of buying off-site compared to WDW.