Luggage and bags:
Mt Gambier is a place where you can just about have 4 seasons in one day. My biggest message is - COME PREPARED!! It may say 34, but by 6pm it will be cold. And even though it is raining, it may be rather warm.
Clothing/Shoes/Weather Gear: Bring a couple of everything.
Toiletries and Medical Supplies: Suncream, although you can buy it here if you somehow manage to forget!
Photo Equipment: You can buy all your supplies here, we are not really out in the bush!
Camping/Beach/Outdoor Gear: Fly spray, insect repellant.
Bring a good pair of walking shoes with you to Mt Gambier, especially if you plan on going underground in the caves. Also, there are plenty of walks to take.
Toiletries and Medical Supplies: Anything else you need you can buy in town. There are 2 supermarkets, plus a shopping centre with department stores and plenty of shops in the main street
Photo Equipment: You should be able to buy any film etc that you need in town.
Camping/Beach/Outdoor Gear: It's a great place to camp, especially at the nice caravan parks, so bring your tent and camping gear if you like camping.