Unless I need to run for an overlooked item while brewing. I purchase everything online. The twenty plus mile round trip to a store is not in my budget.
I find answers to any questions or problems I have in forums, blogs, from suppliers and within book and periodicals.
I store 50# bags of grain in 30 gallon galvanized garbage cans. I have had no problem storing grains for up to two years. The grain is kept along the inside wall of our office. The personal computers keep the humidity low and the grain a constant temperature.
Yeast is retained, from previous brews, and fed in pint fruit jar, store in the back of my refrigerator. I've store yeast up to 7 months so far with no change in my recipes quality. Also I have used powdered bread yeast without problem in cream stout.
My oats for oatmeal stout are whole grain purchased from grain cooperatives.
My barley I purchase through wholesalers.
Being creative with brewing supplies just makes the whole process more fun.