I'm on the fence over whether shopping locally weakens the economy or not.
In general, spending more money for the same value is wealth destroying: money trickles up by nature, through a process I'd rather not outline--it involves specialization of services such that a certain portion of money moving through a business always goes to a very small subset of businesses, the most notable examples being energy (oil) and steel. More spending extracts more money from the consumer base in general, and concentrates it in a smaller consumer base.
Based on these assertions, it's reasonable to assume that shopping locally and buying the same kabocha for $15 would make a community more poor than shipping in kabocha from elsewhere for $5. This is a good example: Kabocha needs to be harvested ripe and stored for 3 months to develop flavor; it's no good right off the vine. That means there's no compromises such as harvesting green bananas and ripening them on truck, versus a local supplier harvesting ripe bananas. So what you get is a bunch of people who spend $15 and get 1 kabocha instead of 3 kabocha, as well as a local farmer or retailer who is either a rich feudal lord or beholden to his lords (oil...).
If it's easier for the local farmer to grow apples, but difficult due to soil and climate to grow kabocha, then the most wealth-generating solution here is for the local farmer to grow apples and export them, and the local community buy some of those apples because they're cheaper than growing apples elsewhere and shipping them in. Elsewhere, where a Kabocha can be grown for $2, a farmer will grow a Kabocha and sell it for $2.50 to a distributor who spends hundreds on bulk shipping that comes down to $1.00 per kabocha, and then puts a mark-up of $1.00 on it and sells it to you for $5. Since it would cost your local farmer $14.50 to grow the same kabocha and you'd pay him $15 for it, you should buy imported Kabocha and get your farmer to grow apples.
Books, electronics, and a lot of other stuff have become more of an import item, ordered online and shipped in. Consequentially, Best Buy, CompUSA, and Circuit City have failed. Your community would be served best by then changing tactic: close down those defunct electronic stores, open up something else. MicroCenter is attacking the problem by coming close to, meeting, or beating most online retailers in electronics prices; if you come close enough, the ability to engage in tactile shopping with no shipping delays is a value-add worth several dollars. Many people will go to Barnes & Noble and find a $35 book they like, then order it for $11 on Amazon; but if the book is $35 and the Amazon book is $33.76 with free 5 day super saver shipping, they'll probably pay the extra $1.24 and buy the book immediately.
I've taken to ordering personal care items from Amazon. Liquid starch, $500 ironing boards (with built-in vacuum--the polymer bonds in organic fibers de-link when you get them hot and wet, and then rotate freely until you get them cool and dry, so vacuum lets you rapidly set sharp creases like at the dry cleaner), laundry detergent, shave soap, and so on. Even a $500 serger, although I get the thread locally, and then I order decent clothing online and tailor it to get that final fit. Some of these things are hard to find locally, or cost $300 more.