I'm a huge proponent of not spending more money than I have to (also known as "being cheap" ). Here's a couple of different ways I've saved some green when shopping at the big box bozos:
Go to your local post office and ask for a "change of address" form. They come in an envelope with various coupons, including one from Lowe's for 10% off all purchases, that's power tools, building materials, anything, up to $5,000 ($500 max. savings). Mine's good until Oct. 15th.
If I have to go to Home Depot and drop a grand or two, I'll stop at Carr's the day before and put all the money into gift cards instead. For every $100 you spend at Carr's, you get ten cents off each gallon of gas at the pump. I've gotten as much as a couple of bucks off each gallon with this method. You just have to wait 24 hours for the cards to activate; people at Home Depot are always asking me why I have so many gift cards.