hearty

I'm going on a 5-day river trip with a group of 14 people.  There will be two transportation days prior to getting on the river.  So...I need a bread that will stand up to 7-8 days of storage in hot conditions, and that can handle the rough treatment of being bounced around in a dry bag (a dry bag is like a back-pack that will not allow water inside.)  We plan to make sandwiches, but the bread doesn't have to be sliced loaves.