Backpacker is based on a fashion style popular in the mid to late 90s where people involved in hip-hop wore large backpacks. Originated by graf writers who kept all their cans and nozzles in the packs, the style caught on quick with the suburbanites and rock kids who didn't want to stray too far from their style but still wanted to have a hip-hop flava.
People use it now as a derogatory term for nerd-rappers, hippy-hoppers, and other fringe hip-hop followers, referencing the fact most of the listeners are suburbanites buying or co-opting into a certain style.
It's not about the backpackers or the OG bling blingers, you blind fuck.
oc means 'original crew'.
man everyone's gathering at the dees tommorow, it's gonna be the oc chilling like old times.