Heavy packs make any group slower. Many search areas are near roads or tracks and it is faster to send groups into the bush and bring them back to base for the night, often by vehicle. The requirement to bear in mind when packing for a day search is that the group may have to support themselves and an injured person overnight.
The sensible level of equipment will vary with the season, but will usually include extra clothing and food for each person plus one sleeping bag, mat and tent or fly between the group. This should enable the group to spend a safe night under all but extreme conditions and still benefit from light day packs while searching.