I would say 95% of my material comes from one supply house. However, when it comes to lighting I will shop three different supply houses.

I rarely buy things from the big box stores. If I am on a jobsite and I need a common item I will find the closest big box.

Also, my supply house gives me a 2% discount if I pay my bill in full by the 10th day of the next month. Might not seem like a lot but it adds up. I also pay my bills by credit card which earns me some reward points.