The problem with what you are doing is that you are likely going to totally stuff up your metabolism because you are not eating for such long periods of time.
You need to be eating little and often in order to increase you metabolism. When you don't eat for ages your body goes into preservation mode, so even though your calorie intake for the day is low, your body will hang on to everything you are giving it because it thinks it's going through lean times.
Perhaps you have been eating like this for a long time and your metabolism is already shot? Well, it's never too late to reverse it. Even though you might feel like you are over eating at first, you are much better off to follow a calorie controlled, healthy eating plan. Just google an online weight loss calorie calculator and figure out how many calories you need to be eating each day to lose weight. Be realistic about your goals, don't just think about your vacation, think long term about your health!
A healthy balanced daily food intake would look something like this:
Breakfast: oatmeal made with skim milk and some honey to sweeten (or stevia)
Snack: 1 piece of fruit and a tub of low fat yogurt
Lunch: tuna and salad wrap made with a whole wheat Tortilla
Snack: cottage cheese and vegetable sticks (carrot and celery)
Dinner: Lean protein and vegetables, optionally a small serve of high complex carbohydrate such as brown rice or sweet potato
Snack: fruit and yogurt, or a low calorie dessert
Depending on what the calorie calculator says you would adjust your quantities.
You can definitely lose weight without exercise, but even if you can do 15 minutes a day it is better than none at all. Every extra calorie burned will work in your benefit. If you don't like walking or going to the gym then why not grab yourself a few short workout DVDs that you can do at home. There are so many to choose from that you are bound to find something you enjoy doing.