I have used space bags or the giant ziplocs for packing and they do work great!
I even took my BIG foam pillow in one...last trip, not a cruise.
it worked. when you open the bag the contents just poof back to their original size with few wringles, if they do just hang in the bathroom while you shower to steam them.
that my 2 cents worth on this subject
Packing is becoming quite a challenge...but i don't have to fly to galveston, just a 1 hour drive from houston.
have a wonderful day where ever you are...