Hiya,
It depends on how often you are visiting them I suppose, I fill my feeders and waterers to the brim when I visit. With my first three chooks I had a single 6kg feeder and I think an 8L waterer and both lasted a few days, and with the grit I just chuck a few handfuls into the run to give them something to rummage for.
When they moult I change the food a bit adding left over pasta and growers pellets and when it's freezing I up the treats like corn and oats to keep them warm.