You CAN check your luggage thru to LIH at the CO desk in EWR if you fly on Hawaiian (HA) and poss Aloha, but not sure about GO or others. Works fine on HA, I've done it 3 times over the past 2 years.

But be warned: ground staff at HNL isn't the quickest. last year, I flew into HNL on CO, and on to LIH via HA, but my bags didn't make it on my flight into LIH. Waited for the next flight's luggage to arrive, and ours wasn't in that batch, so I filed a lost luggage report in LIH. The guy there said the bags could arrive on ANY airline's flight, not just HA, and then he promptly closed down the luggage office and left for the night. ( ). And just as my wife was starting to cry (last flight of the night had just arrived, and the pax were collecting their bags from the carousel) our bags popped out of the carousel.

So, I now take enough stuff in my carryon to get me thru to the next day if the bags don't xfer on time. But even if you can't do that, there's a Long's Drug just a couple mins outside the airport, and a WalMart up the road a few more mins, where you can buy any necessities.

Enjoy Hawai'i!