Sometimes I worry I'm "not doing enough," but I think I actually am doing the work I need to at the moment. I do think some day I may be called on to "do more" (or keep doing the same stuff, but at a greater level of difficulty & personal danger).
My abilities lie in the area of finding, reading, synthesizing, & sharing information. I often feel ashamed of how otherwise "useless" I feel, but I'm pretty confident that the best way to be "useful" is to do what you are good at.