The currency used in Somalia is the Somali Shilling sos. Currently only the 1000 shilling note is used, and doesn't go far... a glass of unpotable water will cost 1000sos. The current exchange rate of 100 US dollars to Somali shilling is 3,300,000 as of May 2008. Much more useful is goods with which you could barter.
The Bakaara Market Somali: Suuqa Bakaaraha is a Mogadishu open market and the largest in Somalia.
Bakaara Market in the heart of Mogadishu. The market was created in late 1972 during the reign of Siad Barre regime. Proprietors sold and still sell daily essentials including staples such as maize, sorghum, beans, peanuts, sesame, wheat and rice, petrol and medicine. Despite a new Coalition government taking control, Somali markets continue to operate largely in the absence of regulations. A wide array of weaponry is also sold, with guns sometimes being the only thing for sale at some markets. Currently, 80% of Somali males own a weapon. Be very cautious, as customers will often test their new weapons by firing into the air. In the markets, an automatic rifle is usually available for purchase for around 1,000,000 sos or $30. even if you think it is macho, don't buy one. you are a lot more likely to use a weapon if you have it, and this would be seen as very bad in the eyes of the law, and could lead to your execution.
There are many things to buy here but be wary of cheap pearls as they may not be real. There are many good tailors in Somalia and it is a good place to have clothes made to measure and copied.