As a previous poster noted, it depends on how well I know the spot in which I'm fishing. Most of the time I take one microslit box, one spool of tippet, one spare leader and some floatant. When I travel to fish, or fish a venue that I am not very familiar with, I go all out. Two boxes of dries, one box of nymphs, a box of terrestrials, a box of streamers, a small emerger box, fluro in 2-8x, forceps, thermometer, seine, collection jar, knot tool, dry and gel floatant, tin shot. My 'travel' kit includes all of the above, a 4wt cane, 5wt SLT, and 6wt Z-Axis. And, of course, rain gear, sunglasses, hat, smoke and some drinks.

That being said, nine times out of ten, it's just me and one box and a pocket full of junk.