Camera, lenses, bins, scanner, log book and reference books, tripod and/or monopod, cleaning accessories, spare batts, charts, compass, passport, money and a toilet roll! (The latter, believe me, is up there with the camera and lenses...Man, have I been caught out before!) Sometimes have the spotting/drinking beer chair too! Oh, and a set of steps in the boot too!
EOS1D4, 7D, 30D, 100-400/4.5-5.6 L IS USM, 70-200/2.8 L IS2 USM, 17-40 f4 L USM, 24-105 f4 L IS USM, 85 f1.8 USM