I can be a bit pedantic, and the Gaffer District campaign referenced in the title bothers me a lot. Shop (a verb) can only be modified by an adverb, in this case locally. English is the most wonderfully rich and nuanced language there has ever been. A slight change in word order, a comma here or there, can completely change the meaning of a sentence. Using an adjective instead of an adverb may be catchy, but it is meaningless and demeans the language.
With that off my chest, I will talk about shopping within a limited area, or locality.
The Gaffer district obviously began the push for shopping locally because of the boost to local businesses. The sales tax helps as well. Shopping locally for food means supporting the farmers markets, and buying seasonally. If you buy strawberries in January, you can be certain that they have been flown in from California or another country. They have been kept in cold storage and are pretty tasteless. But if you wait for locally produced ones, you will learn - possibly to your surprise - what a strawberry should taste like. The same goes for tomatoes which, incidentally, should never be put in the fridge. By buying out of season not only are you paying a premium for inferior produce, you are encouraging fossil fuel-heavy transportation.
That applies also to buying stuff online. It has to be shipped to you using both excessive fuel and packaging. There are some things that one cannot find locally, but very little that cannot be delivered in an ecologically friendly way - as long as you have patience. More often than not, a local business can order what you want, and have it included in their next delivery. I see an opening for a new business here. Take orders from catalogs, consolidate them into one shipment and hold for pickup (or local delivery for an additional fee).
Let's support each other.