Jack-o-lanterns aren't just symbols of the season, they can make a great costume, too. Have you considered taking on a scarecrow-like appearance and trying out a pumpkin head Halloween costume? There are a few different ways to go about this classic look:
Wear a plastic pumpkin on your head (or a real one, if you can stand the smell) that's carved out to look like a jack-o-lantern. Think of it as a mask that covers your entire head.
For the rest of your body, you can wear traditional scarecrow garb. This is easy enough to make because all it really requires is old clothes. If you don't have any overalls or anything that looks like it would be a farming outfit, then you can probably find something along those lines at a thrift store.
Maybe you want to go more for the "crazed killer who happens to wear a pumpkin as a mask" theme. In that case, you can either carve out a pumpkin with a mean smirk, or you can buy a surreal plastic pumpkin head with a more elaborate expression.
The clothes are up to you, but something common and mundane might make the costume more unnerving. After that, choose your weapon: a machete or a scythe might be a good choice since it fits with the whole harvest season. You could say that you're a reaper of human beings.
Add a splash of fake blood if you want further realism. Really, there are so many things you can do with a costume like this. So if you want to celebrate the harvest with a vegetable (or is it a fruit?) on your noggin, consider wearing a pumpkin head Halloween costume this year!