The Shovel will be used to dig the hole in the Kaya Forest to get another item in Nabooti Island. This also has a name (Vince Graves) and a phone number (555-6789) carved into the handle.
How to get the Shovel
As soon as you arrive on Giza, open up your backpack and put the Desert Turban on. This will disguise you to look just like one of the tomb raiders digging at the pyramid. Walk over to the first one and he will give you a shovel.