well.. push ups and sit ups certainly aren't going to anything, hun.
exercise is only about 20% of what you need to do to lose weight.. the other 80% is good eating habits.
if you just want to lose a little bit of weight before your cruise.. then..
1) replace snacky foods with fruit or vegetables
2) cut out the juice and soda and only drink milk and water
3) make sure to get a variety of food from each food group every day
4) try to limit your portions.
5) 20 minutes of cardiovascular exercise daily.
Start with about 20 three times a day of each, and do a cardiovascular activity like running, swimming, or hiking. Increase this number by 10 every week. And if you want to lose some weight fast right before your cruise, go on a fad diet like south beach or Atkins. It will help you lose the weight quickly for your cruise but after your cruise, if you stop excercise and dieting the weight will come back fast. If you really want to keep weight off try weightwatchers, my friends did it and lost 30 pounds.