The local currency is the Bahamian dollar B$, but it's tied to the US dollar at a 1:1 ratio and US dollars are accepted everywhere at par. There is thus no need for Americans to change money, and many tourist-oriented businesses will even give change back in US$. Do keep an eye out for the famous but now rare three-dollar bill and 15-cent coin, both originally made to ease the 1966 transition from British pounds to dollars, $3 being roughly equivalent to £1 and $0.15 approximating a shilling.
There is very little made in the Bahamas, but some luxury goods can be purchased at a bargain. Salespeople in the straw market have a very direct but often humorous manner of negotiating the price of a product. A sense of humor is greatly appreciated in this island nation.
Beware of purchasing Cuban cigars. The vast majority of "Cubans" for sale in the Bahamas are counterfeit. Only buy cigars from reputable and dedicated tobacconists, do not buy on the street, in the market, or from rinky-dink combination cigar/liquor shops. Real Cubans cost upwards of $30 USD per cigar. If the price is $10, it's 100% fauxhiba. If you do plan to buy cigars, some online research may assist you in identifying authentic Cubans. The Ultimate Counterfeit Cuban Cigar Primer (http://www.cigarnexus.com...) and The Havana Journal Counterfeit vs Real Cohibas (http://havanajournal.com/...) pages may be particularly useful to you.