The contents of a Warhammer 40,000 Terminator boxset?

I'm creating an army list for my Black Templars army and want to know what's inside a standard Terminator boxset so i can add upgrades. For example, i want to know how many chainfists there are and if i can add 2 ault cannons to my squad. Any information on the contents of the Terminator boxset would be helpful