How to achieve maximum weight loss in 4 weeks?

I'm about to embark another weight lost 'program' for the next 4 weeks. I want to lose at least 10-15kg in that time. Any suggestions for maximum weight lost? I plan to power walk for 30 minutes twice a day, 7 days a week. My diet will include: Banana & gl of soymilk for breakfast, yoghurt & pear for lunch & a bowl (3/4 cup) of bran cereal with prunes & soymilk for dinner. I am 26 years old. Current weight is 75.1kg & 168cm. I know its unhealthy but I need to lose the weight before going on holidays. I plan to eat healthy after my holidays. Please suggest anything to maximise my weight loss over the next 4 weeks without resorting to amputation of a limb haha. Thanks guys =]