In terms of Star Trek, credits seem to only be used for non-essentials.
Accommodation, education, healthcare, food, access to literature, and all the other things a healthy being needs to develop in a wholesome way, are all free, in their post-scarcity economy.
But, things that require more resources in terms of energy, or land use, require Federation credits (perhaps a form of energy credit) - so Kirk's house, being an inefficient building using a lot of land, would be an example.
Some companies, that make luxury/niche goods, like clock-makers, wineries, brewers, etc, may still exist, but without any profit motive - with full democratic control handed over to workers - no wage slavery - no charge for what they produce, other than energy credits - no reason to work for them except out of love for the craft, and perhaps more energy credits - no malign need to advertise or propagandize their product.
Perhaps in order to prevent people inheriting material posessions and becoming covetous, you can't pass things down to children - Kirk's cabin would go to someone else upon his death - or perhaps greed is simply prevented by people being more enlightened about what makes a human life worth living.
Other than that, I doubt Star Trek uses anything like monetary economics (either capitalist or socialist) - rather, it seems to be closer to what Marxists call 'pure communism', or to an anarchist society of collectives without coercion or compulsion, or to a green resource-based economy.
The most important thing is, it is post-scarcity. Most of our economics deal with a world in which money exists or resources are limited.