Smuggling (Dutch pronunciation ) The definition:

• is the illegal transportation of objects, substances, information or people, such as across an international border, in violation of applicable laws or other regulations. (source )
• To avoid IRS-tax (Internal Revenue Service (= the part of the US Treasury Department that collects most taxes owed to the federal government, including income tax))
• convey (someone or something) somewhere secretly and illicitly. (source )
• the crime of taking goods or people into or out of a country illegally (source )

There are borders all around the world.

Borders prevent the passing of areas, people, animals, products and information. They provide protection and can also be the reason for (armed) conflict.

What is there to smuggle?

The answer is bold and bright: EVERYTHING!

It depening on the situation if the bennefits are enough for trafficing the goods over de border. It's just a question of Supply & demand.

That there is no end to the creativity of mankind may be obvious due to the variety of TV programs that are available about this subject.
In the Netherlands that are: Border Security, Road Wars, Police (Dutch: Wegmisbruikers, Politie op je hielen) etc.