"Bikepacking" does not mean use a backpack.

The twist on "backpacking" refers to how you're doing a backpacking-ish trip but on a bike; i.e. a sort of (generally offroad) tour.

"Bikepacking bags" are those specialized for putting a decent amount of weight on your bike, while keeping it all centered and stable. Basically, large handlebar and saddle bags, and frame bags. Relative to racks and panniers this keeps things smooth as the riding gets more technical, although getting rid of racks limits your carrying capacity.