Try looking through this website: http://www.equipped.org/home.htm It helped me decide what to put in my kits. They have a section on different sized kits, and they also do reviews on items that are commonly used.

Two items I like are a Sparklite firestarter (comes with tinder) and dry condoms. The condoms are good for holding water, and don't break as easily as you'd think. The sparklite itself is a lot smaller than one of those magnesium ones, and is easier to use.