As a general rule, its best to turn off all sources of light other than the flash. I use at least 400 speed film in my fully manual Pentax 35mm camera. Normally, I use my flashlight to find the features I want to focus on, then cut the light and hope.
A disposable camera with a flash would probably be the best type of camera to bring into the cave. The environment in the cave is wet and gritty- a sure way to screw up a camera. Next time I go into the cave, I plan on having a couple of those waterproof, high-speed disposables- that way I can be sure i have enough film and I will know that I am not messing up my good equipment. ----NOTE: On my last trip, I used a bunch of disposable cameras, and was a bit disappointed by the results. I will go back to risking my good camera. The disposables are great above ground, and for close-up features, but the flash units in them are just too weak to handle the darkness. The ones I used had a focal length from 4 to 10 feet, and many cool features are out of range.
Some Pointers: If you have the equipment to set up a flash some ways
distant from a camera, you will be able to take some striking shots. One
book I have about photography in caves suggests using up to 32 times the
amount of light normally used in a standard flash. I have found that in
taking pictures of close-up features, the flash was a little too much light-
but in taking pictures of panoramic shots, like trying to photograph a
large chamber, my flash is not nearly enough.