Can you wait and buy it when you arrive? NO
In a tropical climate, and when exposed to germs with which your your body is not familiar, even a small graze can turn septic. Fly bites and other 'itchy' problems are particularly vulnerable and need to be cleaned as soon as possible.
Since you can't expect to be near clean tap water or a doctor's surgery, a supply of antiseptic wipes is a very useful bit of kit. They can be bought either in tubs (like the ones used for baby changing), in small boxes (often sold as hand cleaning towels) or in individually sealed units for First Aid kits.
So long as they are antiseptic the packing style doesn't really matter too much. I like to have a few individual sealed and really strong antiseptic wipes in a pocket, and a small box of milder ones in my rucksack, but that's personal preference.
They are also very useful for cleaning hands before eating, putting over popped blisters, and for wiping the ever present red dust off your face.