We had a day in Noumea, so we took the 10:45am 2 hour Tchuo Tchuo train and did our own thing in the afternoon. As this meets you on the container pier (Spirt is too large for the Ferry Teminal), we should could have gone for an earlier trip to have more time in the afternoon.
The little train is a good way to get a view across the island and provides an overview of what you might go back and see in the afternoon.
We had lunch at one of about 4 cafes at the ferry terminal, all took Credit Cards, AUD or CHF as well as French and English menus.
For the afternoon I picked up a $5 all day hop-on hop-off shuttle ticket from the ferry terminal. They have a range of stops around the island and run every 20mins all day.
I took the shuttle bust over to the Aquarium (15-20 mins), very similar to the Sydney Aquarium at Darling Harbour, but only costing $10 AUD when bought bundled with the shuttle ticket. The acquarium had both large and small tanks with information signs in both English and French. Large tanks where about the size of a large bedroom, not like the underwater walks in Sydney, but providing nice examples of the local fish, coral, sea snakes and reef sharks.
At the main beach there was also windsurfer hire which might have been fun if I had started the day a little earlier. There were probably also more interesting places to eat further away form the Ferry Terminal.