You can't come to the Sahara and not ride a camel through the dunes. Or, I'm sure you can, but would you want to? Also, the signs advertising camel treks - usually accompanied by packs of the bored-looking beasts themselves - are so ubiquitous throughout the region that you may as well hop on eventually.
While you're indulging Lawrence-of-Arabia fantasies on a trek through the desert, it's also a great opportunity to chat with the guides, many of whom speak English and all of whom speak French. By the time you dismount your steed, you'll have had ample time to gather insight on good restaurants, cafes, or hotels at your destination.
Nearly all towns on the Sahara tourism circuit have a "Zone Touristique" where you can work out a trek. While an hour on camelback outside of the town of Tozeur was enough for me, I'm told there are many opportunities for overnight trips as well.