As with early TV shows it was routine for one series to have an exclusive sponsor, this practice ended by the late 60's, many stars even appeared in the commercials.

We all know The first early years of the stones were sponsored by Winston cigarettes! These commercials are easily found on youtube with F&B smoking behind the house.

Then came Pebbles! The popularity and tone of the show changed, so Welches was a sponsor, I never noticed until the MeTV airings how much Wilma says to Pebbles "You love your grape juice" believe it was even said to dino! LOL So yes this was a especially written in product endorsement as then Pebbles was appearing on Grape juice cans and of course the 16 different flintstone jelly jars/glasses that were produced over a three year period and are now valued collector items!

"Keep drinking your grape juice Pebbles, instead of vaping!" LOL

Yeah, she used to say something like "Woo woo gape juice" that I knew was stupid even when I was five.

They also sold a set of Flintstone Building Boulders (styrofoam blocks). Opening credits showed Pebbles playing with the blocks:

https://m.youtube.com/watch?v=XLzYv7Zjuk8

Yes I remember that, back to grape juice, it was kind of obvious advertising writing, as most of their "stoneage products" had "cave names" like cactus juice to simulate alcohol, but grape juice was grape juice! LOL Just imagine Fred asking for a "beer" after work! LOL.....

I imagine you could consider these "cast commercials"