Before knowing what you should not carry to the USA, you ought to know the specific government agency that will pull you up if you carry anything that you aren't supposed to take into the United States. It is the US Customs and Border Protection (CPB) that is directly responsible for enforcing the laws that allow or disallow certain things to be brought into that country.
The officers of the CPB stand guard at all the ports of entry into the United States and keep a close eye on everything that is taken into the country. They will seize any and every item that is prohibited from entering the US like,
Next, there are certain restricted items that will require licenses or permits from the specific government agency dealing with the item category. These are firearms, certain categories of fruits and vegetables, certain categories of animal products and by-products, and also certain animal species.
You will have to find out from the respective US government agency dealing with each of these categories about the procedure to apply for specific licenses and permits. You need to remember that many restricted items are almost as good as prohibited since obtaining licenses and permits for them is near impossible.
Here's a list of many other items that you can't carry to the US-
Going to the United States has become more complicated now after the arrival of President Donald Trump who had promised to cut down on immigration and imports substantially during his election campaign.