Traditions & Customs
Sudan is an Islamic nation, and the government has imposed a form of Sharia law. Alcohol and drugs are forbidden, though many people dip a kind of snuff, and a few make moonshine. Sudanese women tend to wear very conservative clothing and cover their heads, so foreign women would be wise to do the same, even if they observe other tourists who do not respect this custom. Men should wear long trousers, not shorts. If in doubt, play it safe and cover up.
The Sudanese do not expect foreigners to adhere to Ramadan, the holy month of fasting, but it would be tactless to eat, drink or smoke in public. (Many people, e.g., diabetics and those traveling more than a certain distance, are exempt from Ramadan, so it is possible to find open restaurants during the day but they are not well advertised.)
Be assured that any foreigner will be treated exactly the same as a local, and dealt with accordingly, in many cases, given a jail sentence of several months and a whipping, the minimum being forty lashes (it may be more, according to the discretion of the local cleric). Distances between towns or villages being far, and news may travel very slow because of the political unrest, so your government, if it even knows or cares to interfere, may not be willing or able to help you.
Do not under any circumstances show images/statues/figures etc. of the prophet Muhammad. A heated controversy erupted when a British schoolteacher in Sudan allowed one of her students to name a teddy bear "Muhammad", prompting angry protests in Sudan. Although the British school teacher is safe in her home country and no fatalities were reported, other related controversies such as the Pope Benedict XVI and the Jyllands-Posten Muhammad drawings led to violence.
To show the bottom of your foot is an insulting gesture, as is the touching of the thumb to the index finger while extending the rest of the fingers (the North American sign for "O-kay"). Although Sudan is a moderate Muslim culture, foreigners are still discouraged from speaking directly to local women unless spoken to, and even then it would be polite to ask permission from the man accompanying her before responding. Try to avoid physical contact with women if possible.
During conversation, avoid asking direct questions about people's political opinions unless you know the person quite well and sense that they would be comfortable; repercussions could be serious for them. Tact is a necessity in a country that has suffered the trauma of more than 40 years of civil war, and refugees from affected areas are spread around the country, especially Khartoum.