AJ's costumes and jewelry was probably a good chunk of that, plus filming in Venice. Angelina's jewelry was privided by her personal jeweller, who was the former CEO of Asprey.
Stars: 2 x $15 million
Co-stars: 2x $1.5 million
Rest of cast: $1 million
Location rentals. Expensive. But probably no more than $5 million.
Costumes, makeup: cheap
Blowing stuff up: maybe a million.
Crew -- unionized and cashing in on overtime: maybe $10 million
I think the $100 million is the "all in" budget - production (above and below line costs) plus promotion. Because there sure isn't $100 million on the screen.