It is not necessarily the case that you need to get in to a "top school". Obviously it won't hurt but none of the organisations you have in mind are that narrow minded. Whilst travelling I recommend you do a little more than sight seeing and getting drunk. Do some voluntary work or learn new skills, maybe scuba diving etc. you need to demonstate a level of drive, imagination, commitment etc, lying on a beach all year won't achieve much.
Smurfit is a decent enough school, the reality is that if you haven't already got excellent academics from school and your first degree you're going to struggle getting into top tier mgt cons.
Enjoy the year off! (byron bay on the east coast of aus is bloody great)