My son loves Taco seasoning, so I buy the big container at Costco for that, otherwise grow my own (herbs and chilies) or buy bulk from my local organic grocer.
My one exception is a bag of Italian seasoning that I keep in the freezer. I originally had a gallon zip lock of it, am down to less than 1/2 now. We use it in Pizza (every week) and spaghetti sauce.
Baking spices, cloves, all spice, cinnamon nutmeg, get rotated every 2 years or so. I buy whole and grind to get a bit more life from them.
Indian spices are kept whole, then toasted and ground. But sometimes I buy prepared garam masala.
Baking powder and soda are used up quickly, generally within 6 months of purchase.
I keep gingerroot in the freezer and grate it from frozen into whatever I am preparing.