Luggage and bags: Try to take as little as possible to Tanna Island...the plane from Efate is only small... We packed our things into one suitcase and left the other at a resort in Port Vila.
Clothing/Shoes/Weather Gear: Light and casual clothing is about all you will need. Plus maybe one pair of long pants and a light jacket.
Toiletries and Medical Supplies: You should bring most stuff from home or buy it in Port Vila before going to Tanna Island - you won't be able to buy a lot of things there...including snack foods, medicines, toiletries and any other 'conveniences'.
Photo Equipment: Take lots of film or huge memory cards! And a tripod will come in handy too...especially if you go to the volcano at night.
Camping/Beach/Outdoor Gear: Insect repellant with DEET in it is a must...as well as sunscreen and lots of it!