Smeyers

Look through the cruise compass section of this website and find one from your ship and correct number of nights.  It should be pretty accurate.  Theme nights can vary based on different cruise directors, location of sailing and number of nights. 
On a 7 day cruise there will typically be 2 formal/dress your best nights and 1 tropical night if you are in the Caribbean.  These are suggestions only and you will see a lot of people wearing whatever they want.  Nice casual is always a safe choice for any night.
A lot of ships also will have a 70's disco party that some do dress up for.

.......... in the US.
Actually, it is correct to enter some, currently not all, EU member states or board a cruise ship departing from ports within EU member states. The salient point is that in some EU states the "vaccination record" is only valid for 275 days. The broader EU regulations published in February 2022 do not state from from which vaccination date, initial series or booster. However, that varies from EU state to EU state.
For example, if your booster was administered on January 1st, 2022 and you are traveling and planning on cruising from an EU state that still requires a valid vaccination certificate after October 3rd, 2022, your CDC vaccination record would only be valid if you had received a booster on or after October 3rd.
Admittedly, this issue for EU travel can be confusing. That is because not all member states have the same rules for proof of COVD vaccination. The rules have also changed since I traveled to Europe in April and upon which I based my point of clarification. Few EU states have any proof of vaccination requirement to enter and those that do have varying wording.
Here's a link to an EU sponsored web site that allows you to set your departure country and planned country of EU entry and find out what the COVID related entry restrictions are.
https://reopen.europa.eu/en/from-to/OTC/ESP
What's interesting is that most EU states, as of June, 2022, have lifted the requirement to show proof of vaccination to enter entirely. Spain and Luxembourg, two EU countries that still do require proof of vaccination to enter, use different wording to describe what is and what is not considered valid proof of vaccination.
Finally, your correction to my post is mostly accurate for travel in Europe as of the current date - the 275d expiration on the validity of your CDC card, if it has to be shown to enter, is based on the "initial series" or "initial pattern." It is still a very good idea if you are traveling to Europe to pay careful attention to COVID related entry requirements. They can change on a moments notice and if there is another surge in new COVID cases this fall - something that many epidemiologists are forecasting, proof of vaccination will almost certainly be required again.
      

Sorry I actually didn't see that you had quoted a different comment. I am sorry for my reply to you. 

This is actually incorrect. "Up to date" is defined as full dose (2 shots for pfizer, moderna, etc., or 1 shot for J&J for example) of the vaccine up to 270 days. If 270 days have passed since your full dose was completed, then you need a booster to be considered up to date. The booster does not expire for being considered "up to date", meaning I got my booster a year ago and I am still considered up to date.

Could you use a photograph? Yes. A friend of mine did on Navigator (though he had the physical card, too).
 
Would I rely on that to be the case, nope. Have the physical card.

I started this same thread a few weeks ago before my cruise.  I was never asked to show my card at any time.  The picture i uploaded on the app was all they needed.  It could all depend on whoever checks you in but I wouldn’t worry if you have the picture and it all matches your other documents.  
Don’t listen to the people who tell you they demand a physical card,  those same posters said that to me and it was not true.

I'm just ready for the official guidance to come out this week.