The correct answer to this open question is the following.
The items that are usually considered contraband in war are weapons and articles used for fighting.
Contraband is an illegal introduction of articles or products into a country. It is penalized by the law of the country. It is called contraband because the introduction is not legal and the articles do not pay taxes. For instance, during a civil war in any country, the illegal introduction of weapons can benefit a guerrilla or rebel group against the military troops of the country. That is why the government forbids it.
