With an average American adult weighing 180 lb (good God), plus 5-10 lb of clothes and personal effects, add on 50 lb of luggage, you’re at 240 lb per passenger on a full flight.

So you could add on another 50 lb luggage and they’d still weigh less than a shuttle and the bins of rocks, give or take some snacks. 

 @PunishedD 
As a data point, I usually travel with two bags - roughly 80-90 pounds total. Plus you are ignoring freight like mail or other items.

@7bcc0e3c