In the box is every slide, bracket, bolt, and board you need to assemble and install your drawer. You'll be sliding and organizing in a couple hours.
What is excluded are the customizations such as wings, fridge slides, carpet, paint, cutting boards, power systems, lighting, bottle openers and your cool ideas I can't even conceive of.
My advice is to enjoy the journey: start with 1 or 2 Reef cores, then pack out on a few trips, see if you need the space on the side to get your chairs to fit, or would prefer wings. (keep in mind you can't open them while loaded!) Or if you have a fridge, think about our slide module. Fire extinguisher? Think about the "Emergency" Front panel. (and if you don't have one get one right now!) Play, have fun, see how your Reef grows.