Cordon off the incident area with surveyor Plastic Flourescent Marker Tape or crime scene tape. You can often find single rolls of this tape at Home Depot or Lowes or your local hardware store. Treat the location as if it is a crime scene.

If the subject touched anything, (hurling rocks or boulders, disrupting camp, handprints on windowsills, glass, etc.) leave things where they lay until you can collect and bag the evidence properly.  If it is dark, wait for light. Use latex gloves to prevent contamination of the evidence.

Keep samples separate and uncontaminated.

Place important photographs, videotapes, recordings, or other such evidence in water-tight containers for transport back to headquarters. 

Use a GPS receiver to document location of each piece of evidence. The latest GPS receivers can locate to within 10 feet or so. Document camp locations using the GPS for future expeditions.

Use a range-finder to estimate the distance to the subject or incident so a size comparison can be made.

Use Two-Way radios to relay important information back to base camp or to other members of the team.  Keep your noise to a minimum.

Set up surveillance equipment before making camp

Each team member should have a GPS to prevent getting lost, and a radio to be able to call for help in the case of an accident or injury.  It can also lead others to your location to help at an incident scene.  They can relay the last known location of those who are waiting for your return.  Always travel in pairs for safety.

Make sure you have a complete first aid kit with you

Carry a battery powered weather-radio to track possible storms in your location.

Always carry plenty of batteries, film, digital camera storage, or video tapes.  Never record over any already recorded items until they have been transported back to headquarters and gone over by a team of experts to determine if there is any information on them that is of value.

Make sure you have plenty of matches.  Make sure you use safety when making any fire.  Make sure it is out before breaking camp.  Use water to douse the fire and stir the ashes.  If you can get away without using a fire, this is a better method for your field research.  MRE's will allow you to avoid cooking.  Sterno is better than a fire.

Use a hand held voice recorder to record your voice as well as sounds and voices of others during your hike or during an incident.  Use of a parabolic microphone is even better, especially if you have it hooked up to a recorder.

Use night vision goggles if you are moving around at night.  Even while in camp you may be able to catch movement outside the perimeter if you are wearing the goggles.  This allows you to see in the dark and you don't have to have a fire for light. Using the head type allows you freedom of movement and continuous coverage without having to pick up the binoculars and point.

Bring along a laser pointer for that occasion when you are trying to direct your team members to look at something in a location in the distance which is difficult to see. it also makes it easier to direct others to evidence.

Use the same care you would to prevent bear attacks unless you are deliberately trying to draw the creature in.  Keep food supplies hung in trees at night and bury your trash or carry it out with you.