If you go to Santiago de Compostela, there's always mandatory things to do, like visiting Saint James tumb, taste tarta Santiago, and of course, enter a tapas bar and get some local and excellent food.
Lacón Fumado is a must. It's the pork's forefront leg, lightly smoked, and aged for a couple of months. Then you cut it from the piece on rough bits.
Get it with Ribeiros, the local white wine, served on a special kind of mug/bowl, and bread.