What is a specific word to describe necessary products that customers buy infrequently?

In British English, they're

consumer durables
Manufactured items, typically cars or household appliances, that are expected to have a relatively long useful life after purchase. (Oxford Dictionaries)

Sometimes they're called durable goods, or just durables (durable being defined as able to withstand wear, pressure, or damage; hard-wearing).

Consumer discretionary goods:

• goods and services that are considered non-essential by consumers, but desirable if their available income is sufficient to purchase them. They include durable goods, apparel, entertainment and leisure, and automobiles. The purchase of consumer discretionary goods is also influenced by the state of the economy, which can affect consumer confidence.

(www.investopedia.com)

Well, I seriously doubt an espresso machine can be considered as necessary unless you own a coffee shop. That being said, a necessary item can be termed "necessity," while any product that can be bought to satisfy wants and/or needs would be a "commodity." In economics the term "necessity goods" is used to describe those items we cannot live without.

Durable sales are a good indication of an impending economic downturn. When there is uncertainty, folks tend to hold off on replacing the durable goods in the household. This also includes vehicles.