Humorously after not to have two pennies to rub together and variants, which mean to be very poor, the phrase not to have two yachts to rub together is applied to:
– a rich person complaining of having insufficient means of existence;
– a person who is merely free from financial worry.

These are the earliest occurrences of not to have two yachts to rub together that I have found:

1-: From The Fresno Bee (Fresno, California, USA) of Tuesday 30^th June 1936—an editorialist wrote that, according to the “American Liberty League ¹ publications”:

The American millionaire to-day lives a perfectly terrible life. Some of the poor fellows actually have not two yachts to rub together. Others are down to six or eight automobiles. Still others have had their freedom so curtailed by the dreadful Roosevelt administration that they find it difficult to make the round trip from New York to Palm Reach oftener than six times a year. And nearly all of them are on the verge of nervous breakdown as a result of so much worry about the constitution.

¹ The American Liberty League was a U.S. political organisation founded in 1934, primarily composed of wealthy business elites and prominent political figures, who were for the most part conservatives opposed to the New Deal of the Democratic statesman Franklin Delano Roosevelt (1882-1945), 32^nd President of the USA from 1933 to 1945.

2-: From The Montana Standard (Butte, Montana, USA) of Thursday 19^th October 1944:

During the late but unlamented depression it was said around Wall street that some of our millionaires didn’t even have two yachts to rub together. But during the early part of the war those who possessed only one yacht did their country a good turn. They turned their yachts over to Uncle Sam for use in fighting the German submarines which lurked just off our eastern seashore. Converted into armed vessels, the yachts were used in protecting our shipping.

3-: From an article about Abraham Michael ‘Abe’ Saperstein (1902-1966), the founder, owner and earliest coach of the Harlem Globetrotters—article by Alf Cottrell, published in The Vancouver Sun (Vancouver, British Columbia, Canada) of Saturday 18^th January 1947 (it seems that “He hasn’t two thin yachts left to rub together” means he is no longer wealthy):

He hasn’t two thin yachts left to rub together, but he has six basketball units on the road this season, instead of one. I also noted that when he pulled a letter out of his wallet, some two dozen ticket stubs fell on the table. When I looked at them enquiringly, he pushed them forward for inspection. They were all personal plane ticket stubs, reading San Francisco to Honolulu, New York to Havana, Chicago to San Francisco, Mexico City to New York, and etc.
At least, he hasn’t come down to hopping freight cars, yet.

4-: From this advertisement, published in the Manchester Guardian (Manchester, Lancashire, England) of Monday 15^th October 1956:

WHAT THE ★★★ FORETELL . . .
You drink with the Stars

When the Films show us the ‘high life,’ a land flowing with mink and money, the ultimate sign of rich indulgence is in close-up. A languid hand, weary with emeralds, pours liqueur Cognac from a bottle labelled Courvoisier V.S.O.P.
This is all very well; but do not assume that Courvoisier is reserved for surtax payers only. Indeed no! Many a host and hostess who simply haven’t got two steam yachts to rub together, keep a bottle of Courvoisier on the sideboard—frequently two bottles, Three Star for the long drink and V.S.O.P. the liqueur. They know that in spite of its princely quality Courvoisier authentic Cognac at 44/- and 52/6 is by no means beyond the dreams of average. With Courvoisier in your glass it is very easy to forget this!

COURVOISIER
COGNAC
The Brandy of Napoleon
★★★ and V.S.O.P.

The variant not to have two Rolls-Royces to rub together occurs for example in Momma’s boy is no Prince Charming, by Al Sicherman, published in the Star Tribune (Minneapolis, Minnesota, USA) of Sunday 21^st July 1991:

The 10^th anniversary of the wedding of Charles and Diana ² is July 29, but there are storm clouds on the horizon. We found these letters in the British newspaper agony columns. They might not be from Chuck and Di, but . . .
[…]
Dear Abie:
I’m going bonkers! I’ve been married almost 10 years. My wife, who seemed just a trifle “interesting” when I married her, is becoming more loony by the day. And thick! I knew she wasn’t exactly a Nobel Prize winner, but I swear she’s not quite as bright as a doorknob.
She rides me constantly about my mum. “Why don’t you tell your mother you don’t care what she thinks?” “Why don’t you tell your mother to mind her own business?” Abie, I know the old dear is no saint, but if I stay on her good side I stand to come into rather a nice thing. Without her I wouldn’t have two Rolls-Royces to rub together.

² Lady Diana Frances Spencer (1961-1997) married Charles Philip Arthur George, Prince of Wales (born 1948) in 1981; the couple were divorced in 1996.