My son never took more than 4-5 oz in a bottle, even when he was a year old. At that time I was working, and would leave 2, 4-5 oz bottles for him for the 8 hours I was gone, and it was alwats more than enough. He rarely finished all 5 oz at once, and sometimes he never even took the 2nd bottle before I got home.
BUT - that being said, I don't know if he "made up for it" when I was home and nursing him.
I would plan on leaving 5oz portions, figure 1 for every 4 hours you will be gone, so 24 hours would be 6 bottles. 48 hours, 12 bottles.
If it were me leaving for 2 full days, I would plan on leaving at least 15, 5 oz bottles, just to be safe! I would probably even want to leave more if I could manage it... just in case we got delayed or something. Happy pumping! Better get busy!