For men, packing is very simple. Most men don't wear make up, so it's just clothing and necessities. The best thing about being a man, is that you don't have to think about how many different suits you need to bring (unless you're one of those who love fashion and cannot bare wearing the same suit more than once). So, I suggest the following:
1. one black suit: for formal evenings. If you have more than one formal evening, bring different shirts and ties. For example, if your cruise vacation has 2 formal nights, you may bring 1 formal shirt and two ties. Proper shoes are oxfords - leather laced up shoes.
2. dress pants and different shirts for smart casual evenings: these are non-formal evenings. If you have, for example, 5 smart casual evenings, bring two pairs of dress pants and 3 tops. This will give you more than enough outfits. You may wear loafers with these outfits. Tie is not necessary, although if you feel like dressing up, you may wear one with a nice sports jacket or blazer.
3. swim trunks, shorts, t-shirts, one pair of sandals, one pair of running shoes: necessary for day time fun.
4. haircut: have a haircut before the cruise, to reduce potential hair problems, especially when you need to get up early in the morning for excursions, come back and dress quickly for evening activities.
5. aloe vera gel: I suggest this for men, because most of them don't seem to know when they have over sunbathed. This results in flaky skin and sun burns. For relief, apply the aloe vera gel, and stop sun bathing when this happens.
