Our nearby grocery store sells "pumpkin spice" spice. It's pretty expensive in the fall/early winter when "pumpkin spice lattes" are all the rage. Some time after that, they go down quite a bit in price, and I usually pick up 1 or 2 per year. Like most spices, it doesn't really go bad, you just need to use more.
Many people use cinnamon, and this compound often contains cinnamon and other warm spices (allspice, cloves, ginger, etc.) So you can substitute it for cinnamon wherever you might typically use that.
You could probaly make your own as well, there are definitely recipes online. It's pretty cheap and easy to pick up a can though, so I go for the 80/20 here.
Here are some common things that I use it in:
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Oatmeal
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Cooked fruits
Brings extra flavor and you're not adding a ton of sugar. Great if you put some slightly-overripe fruit on to simmer for a while for oatmeal. Also good if you put it on some fruit that you're planning on putting in the oven. Could use on apples, peaches, etc. for a mini fruit bake that combines well with vanilla-based ice cream for a special treat. By extension, this would be part of a good pie filling.
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Orange vegetables
Sweet potatoes, squash, carrots, etc.
This brings out the sweetness of these vegetables without being overpowering.