DeathGuild/Thunderdome worked a shift at Arctica this year (and previous years).
Basically it worked like this:
1) Some of us are in the truck and are lining up bags of ice at the edge of the trailer (single bags, block ice, bags of 3, and full bags of 6)
2) Customer approaches counter with dedicated cashier, announces what they need
3) Dedicated Ice runner moves TEN FEET OR LESS to the trailer, grabs the ice and brings it to the front
(Note for #3, the customer is still usually paying/receiving change by the time the ice is in front of them)
4) Customer leaves, wash, rinse, repeat.
That walk ALL the way back to the truck takes seconds, and the ice is there, right at the edge, and still being cooled to a degree by the trailer chillers, it takes them 15-20 seconds TOPS to get that ice. Each register also has a dedicated trailer (unless one is pulled for replacement with a new, full trailer). So what you are really saving is MAYBE 15 seconds or so per transaction, and then you have ice sitting out in 100+ degree heat.
Don't forget if we want to put out the ice people need, we would need to have every possible combo of ice sitting out there, so if we get a run on single bags, those full bags and blocks would just sit there simmering until someone comes along that wants them. I think a bigger speed up for the lines would for people to have their money ready, and not dick around in their drug addled state when we ask them what they want.