This problem here is the expense of self-support. Obviously for some goods (food), it makes complete sense. Others, perhaps, not so much.
Watching the movie "Open Range", which takes place in someplace that seems like Colorado/Wyoming/Montana in the 1880s.
There's an interesting exchange towards the end. The scene takes place in the general store, where one of the characters is purchasing the best cigar and candy the store had. He ends up buying a pair of cigars from Havana, Cuba, and some swiss chocolate.
"Melts in your mouth!" "Have you tried it?" "Uh..no" "How do you know it melts in your mouth?" "We can't afford to try it ourselves."
"Don't you want to know how much it costs?" "Nope!" In the end, he bought 3 cigars, 2 chocolate bars and it cost him $5, so $1 each. Quick googling shows that a pound of beef was running about $0.15/lb.
Meanwhile, the other character was thumbing through a china dishes catalog.
So, the premise here is that this shopkeeper was able to import and stock moderately perishable products like cigars and chocolate, as well as make orders for a finished good like china dishes. How long would it take to get the china dishes? Probably, what, 6 weeks for the order to be mailed out, processed, and the china to be shipped back from (perhaps) Chicago?
How long did it take for the chocolate to get across the atlantic, and then shipped (likely by train) to the frontier, and then carted by wagon to the General Store? And, of course, not be melted in to a gooey mess in the process.
6 weeks? 2 months? Of course this is where the wholesalers really make their money. You don't send a box of candy bars from Zurich. You send large crates of them, that a wholesaler buys, and then hands out to distributors, who sells them to the General Stores. Shipping is expensive, and the bulk costs less.
But clearly this frontier town wasn't going to open up a dish factory or a chocolatier.
In Traveller, a system is basically "2 weeks" from anyplace nearby.
With ubiquitous trade, the requirement for self-reliance goes down. The classic "your grocery store has 3 days of food" argument combined with "just in time inventory". I don't need food in my pantry, I'm 2 blocks from a super market and grocery store.
This is a great video talking about this:
https://www.youtube.com/watch?v=3PWWtqfwacQ
Some self reliance is obviously important for security reasons (as witnessed recently with the hurricanes). But with well established trade, short term it's cheaper to ship it than build it. We witness this conflict between the online mega retailers and "brick and mortar" stores, where the convenience vs cost/selection battle rages on.
In So Cal, we've had these "Drive through dairies" forever. Basically, early convenience stores where you drive up, point at your products, and they hand them to you through the window.
They manage to stay in business, even though its $4 for a 1/2 gallon of milk vs $2 in the grocery store.
