Include at least one complete change of clothing and footwear per person. Obviously, all this stuff isn't going to fit "in" your kit, but should be considered. Reduce costs by packing worn or out-of-date items, as long as they'll still do the job.
* Sturdy shoes or work boots
* Rain gear. Discount stores sell inexpensive ponchos.
* Blankets or sleeping bags
* Hats and gloves
* Thermal underwear
* Sunglasses