I think Turkish food is the best in the world, last time I was there I was asked if had gained 10 lbs yet and I had to answer, no, just five.
Two essentials:
Aleppo Pepper
Urfa Pepper
Find the right proportion and mix them with oregano, rub them into red peppers or other veggies with olive oil before roasting them, mix into meats, etc.
One word of caution, Aleppo pepper probably has high sodium. These are not "hot spicy" in my opinion but a much better option to add spice to food than cayenne as that really doesn't have a flavor that is very good on its own.
You aren't going to find these two in a normal store, but fortunately we have the internet and don't need to go to Istanbul to fill up a suitcase. If you do go to Istanbul, go ahead and fill a suitcase and get a much larger variety.
Kalustyan's is a store in NY, on Lexington near 40th? I think they have a web site too.