@Debra Garcia I think most people here have given enough opinions... but I can't restrain myself. Is this first aid kit for yourself? Or were you thinking you might be helping others along the way.
I did bring blister care items, and a few over the counter pain killers, including ibuprofen to help reduce menstrual bleeding (yes, dear readers, that is an approved use of ibuprofen I was delighted to discover!), iron supplements etc. Most of it I didn't use, but was glad to have. I did buy various creams and lotions, and other bits and pieces along the way. The only thing I found somewhat stressful when buying products was that almost everything is "behind the counter". At home, most pharmacies have the majority of their products on display - only prescription medication and some other regulated products are behind the counter. That meant some time with Babbel on my phone.
In Santiago de Compostella, I cut myself on some metal in a bathroom stall. Not exactly an auspicious place to cut oneself. But I asked the hospitalero if they had a first aid kit. They did not have a formal kit, but they did let me rummage through the giant box of leftover first aid material left behind by other pilgrims. I did not get an infection.
If there is a particular brand of something you are used to getting at home, and wish to make sure you have access to on your way... bring it with you.