yipper

You could neatly roll up the dress and suit to fit in your suit case and then have them clean and pressed when you get home.

nukesafe

You might also consider not taking your glad rags on the trip, but buying a used tux from someplace like Goodwill or the Salvation Army. I have seen racks of them for around $30. They might not have exactly your size, but for one night you could live with the shame of not having the trousers break exactly right.

When the formal night festivities end you can throw the outfit away or put it into a charity bin at the last port. I always take my least favorite jacket to Europe for when we plan on eating in fancy places, and chuck it away when we leave.