Use Hoppers (Shutes) To Fill Sand Bags:
Three men will fill hundreds an hour. Load the (Small, because they can be huge) hopper by digger. Simple really. What a time waste that is with a shovel. I’ve seen it done with coal even. Straight on the lorry or truck as well. Like these Small Hoppers. Borrow some, from somewhere, but you get them as lorries also.