Regarding gear for a documentary photography situation, I thought I would use a recent trip I made to central Asia as a case study. I was working for an NGO, documenting the lives of the Kyrgyz yak herders living in the high mountains bordered by China, Tajikistan and Afghanistan. On this trip I had to fit everything (including my clothes and personal items) in my camera bag and one small carry on.
A painter is much more than his or her paint brush or canvas, but without these tools a painter can not share the beautiful art in their head with others around them. A photographer without their camera is much the same. I may have the most beautiful image in my mind or even in front of my eyes, but without at least a simple camera I are unable to share that image with others.