The multicart in that video is the Sean Kelly multi. It's more expensive than some of the newer multicarts, but it includes the full retail library and most of the early Vectrex homebrews. You can press one of the Vectrex buttons on the game select menu and it'll swap to a second memory bank and a second list of games... mostly homebrews. Sean Kelly still sells new batches on ebay occasionally but it hasn't been updated in a long time.
I made a game list/case insert for my cart. Here's what's on it:
Menu 1 - 3D Crazy Coaster, 3D Minestorm, 3D Narrow Escape, Armor Attack, Art Master, Bedlam, Berzerk, Blitz!, Clean Sweep, Cosmic Chasm, Dark Tower, Fortress of Narzod, Heads Up, Hyperchase, Melody Maker, Polar Rescue, Pole Position, Ripoff, Scramble, Solar Quest, Space Wars, Spike, Spinball, Star Castle, Star Hawk, Star Trek, Web Wars, Mine Storm Cheat, Test Rev.4, Frogger, All Good Things (Rockaroids, More Invaders, Vectris, Spike's Water Balloons), Mr. Boston, Tour DeFrance, Moon Lander
Menu 2 - 3D Pole Position, Berzerk 2 (bugfix), Melody Master 2, Mine Storm 2 (bugfix), Polar Rescue Beta (easier, but some graphics glitches), Star Trek 2 (bugfix, pause, new Klingons), Birds of Prey, Disc Duel demo, Patriots, Repulse, Rockaroids Remix : 3rd Rock, Star Fire, Tempest demo, Vector Vaders, Vector Vaders 2 : director's cut, Spike Hoppin, Vectrace, Vectrexians (beta?), Bachs Prelude, Bonnie, Daisy, Engine Analyzer, 4D Rotocube, Mike's Molecules, Hypercube, Figgy, Jukebox