Common GC line items: project superintendent, project manager, jobsite trailer, temporary power, temporary toilets, dumpsters, daily cleanup, mobilization/demobilization, project signage, jobsite first aid, builder's risk insurance.
Typical GC percentage: 8-12% of total project cost on commercial work; 5-8% on simple repetitive projects; 12-20% on complex small projects where supervision is disproportionate.
Don't confuse general conditions with the General Contractor's markup. GCs are real direct costs of running a jobsite. Markup is the profit margin layered on top.