What to pack for Christmas Island

Clothing/Shoes/Weather Gear: Good walking/hiking shoes if you are into nature walks/bushwalking.
Your snorkel and diving gears if you are into these ocean activities.
Light breathable cotton or dryfit clothings as the weather can be hot and muggy.
A raincoat or collapsible umbrella in case water decides to empty from the skies.

Toiletries and Medical Supplies: Insect sprays may come in handy, especially against those pesky mozzies!
And most importantly, lots and lots of sunscreen/sunblock lotion! The rays are deathly.

Photo Equipment: Bring enough negatives if you are still using analogue photography - there aren't that many shops selling them!

Camping/Beach/Outdoor Gear: A good pair of binoculars if you are into birding.

Miscellaneous: And yeah, bring enough Australian dollars for miscellaneous purchases! (There are no money-changers on the island!)