Extra (tried before!) tips to help slim down?:)?

hey:) so my bmi is 20.8, which is okay I know. I'm 114 & 5'2, but I'm goin on a trip to europe in a little more than a week and just wanna look my bee-ee-ess-tee(: I'm thinkin 109/108 ish? I'm doin 20 minutes of cardio a day, a routine that promised me it'd burn 600 calories-ish. and I eat one slim fast, one bowl of special k, and a grapefruit, and maybe a handful of cherrios a day, but any tips that anyones tried before to drop a couple pounds that worked, maybe that might compliment my diet? any tips for metabolism boosting/weight loss in general? kkthankss:)