Well one big thing that European trade brought was delicious, delicious tempura!!

Prior to introduction to this style of cooking in the 17th century, Japanese cuisine had little to no frying with oils at all, except for very occasionally frying fatty pieces of meat. And even then they certainly never breaded their meats, fish, and vegetables to then be deep fried. Mmmm....

The best bits of meat were often roasted or boiled, when Japanese people did eat meat, not fried. Same with vegetables and fish.

The common people certainly had access to this new method of cooking.

They also brought delicious castella cake, introduced around the same time as tempura.

European trade, surprisingly, also brought silk! A lot of Chinese goods were brought from China to Japan via Portuguese and Dutch ships.

Silks would have been priced out of the wardrobes of all but the wealthy and elites. But other things such as more common fabrics like cotton (which was produced in great quantities in northern China), dried foodstuffs, spices, etc would have been available to the common person.

They also brought various medicinal herbs and skins of animals from China, but these were more expensive and would have been more difficult for the average person to obtain.

Raw sugar and sweet syrups were also imported from China.

Trade also brought books, particularly science books, maps, and the Bible.

These books were a great boon to the otherwise sheltered scholars, educated and clergy who were not able to travel outside of Japan for the most part. They kept Japanese elite up to date with various European bases of knowledge, particularly in medicine, cartography, military sciences, chemistry, advances in ship building and sailing in general, astronomy (important because of aforementioned sailing), philosophy, politics, etc.

And of course the Bible. This is important because Christianity affected Japanese domestic and foreign policy a great deal, notably being one of the major factors to the sakoku policy that heavily restricted access to Japan to Europeans as well as restricted emigration. It also ended up being the reason the Portuguese were forced from their lucrative trade route to Japan, since they were sneaking unwanted Christian missionaries into Japan. They were replaced by the much more agreeable Dutch traders.

Books in general did not benefit the common people directly but the indirect benefits to knowledge as a whole in Japan can be argued. Christianity is a less clear benefit, particularly since those who did convert to Christianity were often persecuted and killed. That being said, Christian movements in Japan had several community projects such as building local hospitals in Nagasaki, churches (which became community centers), houses, etc.

And of course, European trade brought whole boatloads of European art.

The cultural exchange between Japanese and European art is evident to anyone by the Edo Period and before that. From early Christian influences to Japonism in Europe later one, this was a huge cultural exchange of art and ideas. It was also an exchange of high quality goods that included paintings, handcrafts, trinkets, etc.

This gave artisans in Japan patronage for their services that might not otherwise have been possible if they were limited to looking for a patron from Japanese lords, particularly during times of war, when the warrior class were ostensibly austere and rejected most art forms.

They introduced a new type of perspective painting, various methods of lacquering wood and metal, a new form of sculpting (many sculpted of depictions of Mary or Christ came with the Portuguese), etc. And of course they introduced new subjects to Japanese painting, poetry, etc.

Many of these new 'style' pieces were then traded to Europeans, particularly lacquerwork and painted porcelain. Gold, silver and copper goods, including straight bullion or coins, but also jewelry, were also traded in large quantities since Japan used to be considered 'rich' in these rare metals (easily accessible mines).

Two things commoners did get were potato and sweet potato.

They didn't seem to have been popular at first. But they became more wide spread in the late 18th early 19th century to combat famine.

Not sure if you want to count this as "European" trade, but first Portugese then Dutch became the intermediaries between China and Japan (who didn't really like each other), bringing in silk and porcelain and such for the elites.

What about diseases? Did Japan or European traders come into contact with diseases that their respective groups had not encountered before?