Jim is right. I also know the customs process very well, and would say that cigarettes and alcohol are not worried about. Do be careful of Cuban goods.
With-out me going into a rant on how sad our emargo is, I'll just say don't get caught with anything Cuban. Much has changed after 9-11, but Bush had told the US Treasury Department to increase vigilance on punishing Americans who flaunt the Cuban-embargo.
They are even starting to enfore the insanely high $$$ fines for Americans who have traveled to Cuba. There are reports the Mexican government is selling passenger lists (flights to Cuba from Cancun and Cuidad de Mexico) to the Treasury Department.
Sure seems odd - at the same time the US Congress is debating the validity of the travel restrictions...what a mixed message. My point is - just don't get caught up in our odd political relations with Cuba!