What are Typical "Big Ticket" materials

Depends on the project, but gypsum board, interior wood or structural lumber, flooring, drop ceilings, glazing, doors, roofing.... I'm sure there are more.

in essence the stuff that costs the most compared to the project percentage wise. Like Tristan said is could be a lot more. In my case I just got a submittal for gravel which turns out to be a major contributor if I can count it. Who would have known gravel could cost a lot. But we have a lot of it and I suggest to work with the contractor to identify the big ticket items on your project. It could also be something that is cheap if you just buy one or two, but if you have llots of it it adds up.