One option to consider is the panniers that are designed to fit over a
Western saddle. This makes for an interesting option to ride or pack. For
example, for a litter carry someone can ride in with soft panniers stored
behind the saddle. Coming out that rider is helping carry the litter and the
panniers over the saddle can pack gear out belonging to the subject and/or
litter bearers. For a deep backcountry SAR, the mounts can pack in spike
camp supplies then be used as saddle horses for day searching. A versatile
option.