It appears that your Grandfather served as an enlisted man in the 6. Company of the 1. Bavarian Foot Artillery Regiment (von Bothmer) in Ingolstadt between 1900 and 1902. He retired as an Obergefreiter, which roughly translates to Lance Corporal. The Stein is inscribed "memories of my service", and from what I understand these were commonly given to people who had finished their term as draftees (since he served 2 years and was enlisted, he most likely did not volunteer - volunteers served only one year and finished as NCOs or officers).

The writing on the pictures are little, not particularly good, rhymes:

"Praised be the crown of weapons, even the biggest army can do nothing without us."

"Where cannons thunder death on death, We stand and watch victory's dawn"

"Today the last shot was fired, for I must go home"

If he was called up to his old unit during WWI, he would have been in 2. Battalion, which wikipedia tells me saw action in Artois, Cambrai and Arras.