Before you travel to Spain there are a few things you should keep in mind.
It is really hot here and the weather is humid, so you need clothes and gear that is more suited for the climate.
You can’t go wrong with any particular type of sunglasses. As long as you can keep the rays of the sun away from eyes you are good.
You could buy sunglasesses when you arrive in Spain so it is up to whether to bring it or not.
Like sunglasses, if you don’t want to get headache or have the sun scorching on your head, then a hat is something you should wear.
If you will be traveling throughout Spain, you need something to keep your body hydrated. A water bottle will help you to keep yourself hydrated and healthy.
If you don’t know any word of Spanish, then you should install a dictionary on your phone.
Spanish people are warm and feisty people. They are not afraid of showing their affection and appreciation of other people. Sometimes small gifts for friends is a nice gesture that can go a long way.
Besides stuff to bring you should know some cultural norms of Spain. Read here on this blog: https://orgonline.travel.blog/2019/08/15/cultural-facts-about-spain-you-didnt-know/