A Typical 1950s Small Town... - Model Railroader Magazine

Many things have already been mentioned.  I'm doing a small town in the Carolina piedmont.  Many of these were focused on a single large industry -- the cotton mill.  With the typical lumber yard, oil, farm supply, and coal, though often by the 50s, the coal dealer was combined with the lumberyard or farm supply.

For business, gas stations (even the tiny town I grew up in had Gulf, two Texaco, Esso, Phillips, American, Atlantic, and Pure, with several of these really being pumps added to general stores (kind of a 50s precourser to today's gas marts).

In the town proper, grocery, drug store, barber shop, cafe, Post Office.  Banks would be in a little larger town, as would theater.

One thought is to keep key store names common to the location and era.  For example, for your NM region, I'm thinking Shamrock, Sinclair, would be more indicative of the location than Gulf which was common in the south.