In terms of those with a talent, like songwriters, they’ll make significant amounts doing that under the publicity radar.
Others employ smoke and mirrors, other streams of revenue, and there’s also the fact that if you have a ‘name’ you’ll find companies happy to give you free stuff in return for promotion.
In my 20s I worked as a model for a specific subculture. I was never famous in any real sense of the word but I got a few front covers and I was known to a degree. I never went down this particular avenue, but women certainly use their ‘known’ status to leverage a higher ‘wage’ in exchange for certain services. I had one London photographer offer me £10k to go to Dubai for three days, saying that he could arrange it to be a regular gig several times a year. There are also European destinations. Like I said, I declined because I never had any interest in, or need for, the sex industry. It does exist though, and plenty of women celebrities do go down that route. Not just Z listers either, because if you play that particular game you can use the connections made to generate more interest, publicity, and opportunity.
The free stuff is a big one too. From actual possessions (clothing, handbags, cosmetics etc), trips away, hotel stays, dental work, aesthetic procedures…you can get all of these in exchange for being seen at a ‘hot’ venue and/or being used in promotion.