The back seat is just a smol pack, the name is a meme anyways.
It's meant to provide the player with multiple different things to do, and allow expandable play, allowing new mods to be added as we see fit.
Whether you enjoy magic or tech, there are some avenues for you to pursue with this smol pack. Also, bees, because bees.
Say you wish to explore the world(s). There are a few mods provided for you to do so, RFTools (if you want to create your own), Aether Legacy for a heaven-like experience, and the betweenlands, for a dark and murky experience.
Maybe you wish to be a magic user? Angel of Vengeance (healing oriented magic), Botania (FLOWER POWER!), Astral Sorcery, VoidCraft, and Thaumcraft all have you covered.
Technology? RFTools, Mekanism (x5 ore processing), Applied Energistics, and Thermal mods all have you covered there.
Farming? Pam's, Forestry, and Agricraft look to be your methods here.
If for some reason you like bees (which is totally understandable), we have Forestry, Magic Bees, Career Bees, More Bees!
Maybe you just like building? Quark, Chisel and Chisels and bits are here for you!