I don't know who refines their gasoline. I found this answer on the Google:
Smith's Gas Supplier
It basically says that different Smith's stores may use different suppliers, many use Shell, and Smith's can change suppliers every year.
If you want cheaper groceries, Grocery Outlet and WinCo are the best.
We stopped going to WinCo when our kids were small because it's hard to bag your own groceries while tending toddlers, but our kids are older now and we recently rediscovered WinCo. I was blown away by how cheap stuff is there. Also, I love all WinCo's bulk foods.