This is a great starter list of books for Norse & Celtic mythology, history, beliefs, and traditions.
The Original Folk and Fairy Tales of the Brothers Grimm: The Complete First Edition
The Tradition of Household Spirits: Ancestral Lore and Practices
Scandinavian Folk Belief and Legend (Volume 15) (The Nordic Series)
Trolldom: Spells and Methods of the Norse Folk Magic Tradition
Icelandic Folktales and Legends (Revealing History (Paperback))
The Agricola and Germany of Tacitus, and The Dialogue on Oratory
The Poetic Edda: Stories of the Norse Gods and Heroes (Hackett Classics)
The Saga of the Volsungs: With the Saga of Ragnar Lothbrok (Hackett Classics)
Myths and Symbols in Pagan Europe: Early Scandinavian and Celtic Religions
Here is a link with all the books added to one shopping list, for anyone interested.