Some of the movements we program have no true substitution.
They are odd object movements that have inherent instability that activate muscles that a barbell can't fully replicate. Most of the substitution questions we receive are sandbag related.
We suggest either buying a sandbag or making one on the cheap out of a sandbag and 100 mph tape, because honestly there's nothing like moving a sandbag. However, we realize that certain gyms don't allow certain movements, space is limited, or equipment isn't available.
Sandbag ground to shoulder -> atlas stone ground to shoulder -> double KB clean -> power clean
Lateral sandbag throws -> lateral KB throw -> lateral sledgehammer strike -> KB chop -> lateral cable chop -> lateral med ball toss (triple the distance)
Over the shoulder sandbag throw -> over the shoulder atlas stone throw -> over the shoulder KB throw -> over the shoulder med ball toss (triple the distance) -> power clean
Back rack barbell carry -> march in place with barbell (1 step equals 3/4 of a meter)
There is a way to train for rucking without rucking and that's trunk work and cycling.
For swimming, you can sub in running, rowing, or cycling (including stationary bike). Multiply the swim distance 4.25x for rowing, 4x for running, 12x for cycling.