Yes, the spice mix is the whole deal, you can do anything you want. I am a cheapskate and don't do exotic ingedients - think much of what's at Costco. And I have no authentic chili experience, but here's what I'm currently doing.
I usually use frozen ground beef patties (Costco) just because it's convenient for me. A lot of fresh chopped onions and garlic, sweated or browned with the beef. A lot of normal McCormick chili powder (Costco size), like 1/4 cup for a 3 quart final batch of chili. The tiny bottles of it aren't going to cut it. McCormick is pretty mild, so I add some cayenne and pepper flakes for the heat. Some people will do combinations of various dried/canned chilis. A good spoonful of ground cumin, like a tablespoon for my 3 quart batch. Cumin is a very common chili flavoring. A pinch of Mexican oregano. Some salt to taste - probably not a low-sodium food, you need some salt. Many people add some masa corn flour (used to make tortillas) as a thickener, just be careful to use a technique that avoids lumps. I seldom keep masa around, so I use a spoonful of corn meal, which ends up grainier, but doesn't bother me. I even add a can of beans if I have it around. I do add canned tomatoes, partially pureed in the food processor or blender. Some people will also add tomato sauce and/or paste.
Some people mention ingredients like a little coffee, cocoa powder, beer, soy sauce, etc but I haven't found these to my liking.