Headlights
A headlight is an excellent piece of gear to bring for each person on the trip. You can wear it while eating in the dark, sitting around the campsite with friends, or when you need to go take a toilet trip at night. Headlights have become much smaller and lighter in recent years while maintaining the same light output.
For car camping, or for those who don't mind a little extra bulk, a battery-powered lantern is a nice addition for sitting around the campsite talking and relaxing.
Water Filters
Most wilderness campsites are located near some sort of water source; however, the water source may be low, and its cleanliness should always be treated as suspect. Bring a water filter so that you can have cool, clear water from the stream or lake that serves as the water source. A good rule of thumb is to have one water filter per two people.
Boiling water is as effective as a filter is, but it takes longer and then the water isn't cold.
Camp Chairs
Whether you are hiking to a remote campsite or car camping, a camp chair of some sort is a great convenience (see Resources). Some are designed to work in conjunction with your sleeping pad and are much more compact and light as a result.
First Aid
Bring a well-stocked first-aid kit that includes a variety of bandages, dressings, blister treatments and pain killers, and know how to use them.