Luggage and bags:
Most of these deals you can find include hotel and airfare. Remember that your bags will probably be limited to 20 kilos each. Pack light so you can bring home the souveniers for all your friends and colleagues. :)
Clothing/Shoes/Weather Gear: It's not so warm in Tunisia in winter. It's warmer than Europe, but I still required a winter jacket and sometimes even a scarf and hat when the wind picked up -- especially at night! I recommend having layers, so you can remove some in the hot sun, and then put them back on as the temperature drops.
Also, your beach/pool shorts won't go over so well in town, so bring lots of pants and dress conservatively.
Photo Equipment: Don't forget your camera charger!!!
And bring extra photo cards or your laptop to download those photos. I found you can take a LOT of photos in 2 weeks!
Camping/Beach/Outdoor Gear: Maybe sunscreen? The sun in Tunisia is very warm!!!
Miscellaneous: A water boiler is always good to have!
Bring plastic bags, like the kind you would get to carry your groceries home from the store. You will undoubtedly get sand everywhere, and you can minimize that a bit with the bags. You know, like you could take your shoes off outside your door and put them in a bag before walking in your hotel room and tracking sand all over the floor.
Luggage and bags:
Bring your clothing etc in two bags and split it equally between the two, if one goes missing then at least you won't be stuck with nothing to wear.
Clothing/Shoes/Weather Gear: Round the pool - Topless sunbathing is tolerated but you will get stares from the staff. Otherwise large sarongs/kaftans as cover ups for when going to the bar etc in the hotel. Walking through the hotel in a bikini is sure to attract unwanted attention. Loose kaftan type garments are pretty cheap in tunisia so you should be able to pick up some whilst you're there.
Out and about - Cotton clothing, leave the synthetics at home! Women will be much more comfy and less likely to be hassled if you wear a tunic type top and cotton trousers, mini skirts and bikini tops should be left in the hotel. Wear a hat to avoid the worst of the sun.
Trips into the sahara - long cotton trousers and long cotton tops for men and women, the sun is fierce and it will stop the camel fleas from biting if you go on a camel ride in Douz. Also for women it stops some of the stares.
Toiletries and Medical Supplies: Take some rehydration sachets, even in the best hotels it is easy to get a stomach upset and these will help you get better much quicker. If you don't have any then a teaspoon of salt and a teaspoon of sugar mixed up with water and a bit of lemon juice is a good substitute. Also flat regular coke is a good alternative.
Lots and lots of high factor sunscreen! You don't want to look like an overdone turkey so take it easy with the tanning/burning.
Bring or buy the local shoes, your bathpack, a hat, sun lotion, after sun cream and your all set :-)
Toiletries and Medical Supplies: Imodium (or some other diarree-stoppping medicine)
Photo Equipment: A good flash: the sun is always present and using a flashlight; the light balance is easy restored.