Tell Dave not to get worked up about the Captain's night. The Captain's night isn't anything near what it was when I first started cruising in 1981. You will see all sorts of dress, particularly on shorter cruises people don't dress up as much. You may see those who really like to dress up and those who don't. If a sports coat and tie with slacks is too much for him, then polo/Hawaiian shirt and dockers will probably fit right in with what some are wearing. Sadly, times are changing and the airline luggage fees aren't helping.
Read your daily program each day, circle or highlight the things that interest you most. Everything is quite simple if you just read the program. The important thing to remember is you can't do it all, so just enjoy and have fun.