While I am not yet aware of the extra's on this DVD set, I can tell you this about the 2nd season (1961-62). The 2nd season helped better establish the modern Stone-age family. In at least 6 of the episodes, Mel Blanc was absent due to illness so Daws Butler had to supply Barney Rubble's voice (thus making Barney sound more like Yogi Bear). New characters introduced are Mr. Slate, Fred's no-nonsense boss (voiced by John Stephenson; Mr. Slate had one cameo in the 1st season, but didn't look or talk at all like the Mr. Slate you probably remember), Arnold the smart allecky paperboy (voiced by Don Messick), Joe Rockhead, an alternative buddy of Fred's and Mrs. Slaghoople, Wilma's "battleaxe" mother (actually, Wilma's maiden name started out as Pebble but that name probably went out the window when their child Pebbles was born).
Highlights include a voice cameo from Hoaggy Carmichael (Fred warbles a cheezy rendition of "Stardust"), Fred and Barney not speaking to each other after Fred insults Barney ("Did you get the lisence of that truck, Betty?"), Barney gets a job working for Fred's company since Mr. Slate finds out he's his nephew, Wilma gets a job as emcee of the TV series The Happy Housewife Show leaving one not-so-happy husband to get his own dinner ("Make your hubby happy, keep your hubby happy... with Rockenspiel!"), Fred and Barney are judges of a beauty contest and women across town are trying to get their attention (leaving 2 understandably jealous wives), Fred goes on a gambling streak which winds up owing paperboy Arnold lots of money ("BET! Bet, bet bet...."), Dino gets a part on the Adventures of Sassie show with fred as Dino's agent ("At the end of the show, even the villains smile!"), Barney coaches a Little League baseball team and Fred volunteers as umpire ("I call 'em as I see 'em"), Barney and Betty stay at the Flintstones' house after plumbing problems but it isn't long before their welcome is worn ("Shhh, the girls'll think we're fightin', Fred"), Wilma and Betty get invited to the Ambassadors' Reception but neither they nor Fred and Barney are well received since they're not rich snobs (that is, until Fred and Barney unwittingly prevent a burglary), Fred writes a vitriolic protest letter to his boss when he doesn't get the raise he expected (Wilma saves the day here) and Barney plays a practical joke on Fred ("You, Barney Rubble, are a counterfietter!").
The 1st season helped get the Flintstones started and the 2nd season had the characters better established for Fred (Allan Reed), Wilma(Jean VanderPyl), Barney (Blanc) and Betty (Bea Benederet).