One of the biggest challenges in fly fishing photography is something you have the least control over: the weather. Fly fishing will take you to some sweltering locales and some downright frigid ones. No matter what the extremes, all can cause a problem for cameras when transitioning from your tent, cabin, or motel to the outside environment. Typically the temperature and humidity is such that simply taking your camera out from one to the another can cause lens fogging and internal condensation.
As I noted a couple of weeks ago, one solution is simply leaving your camera in the outside environment for a couple of hours before shooting. But another way -- favored by many pro photographers -- is to make a permanent home for silica gel or desiccants within a waterproof pack or bag.
These products can be bought at most high end camera stores and are fairly compact items, easily slipping in a camera bag. They range in price from anywhere from a couple of bucks up to $30 or $40 dollars and work by sucking the moisture off of items and containing it within themselves -- kind of like rice does in salt shakers.
But if you're like me, free is always better. I've found that my local pharmacy has an endless supply of silica gel and desiccants in every shape and size you could conceive of. Apparently almost every drug in the world comes packaged with them and pharmacists just throw them out. Next time you're in need of some camera drying magic simply roll on down to the pharmacy and ask for their extras.
I used the Silica Gel packets that I found in stuff I bought for helping prevent condensation and moisture damage to my camera. The problem is that most of the time the packets are completely saturated by the time they get to you. I found a great source for inexpensive packets that can be reused: www.silicagelpackets.com. Having ruined my share of cameras and phones, it is well worth it!