At least one month prior to departure

Arrange for any needed wilderness permits, fire permits, or permits allowing you to take research samples from private or protected areas.

Get additional travel insurance if needed.  Make sure it includes international evacuation, emergency health care, and property coverage.
Arrange for time off from work. Get inoculations or shots if needed.

Arrange for transportation to/from.

Get EXTRA personal medications if needed.
Maintenance check on vehicle(s). Arrange to have a friend, family member, or professional service care for the pets, plants, and kids.
Advise anyone who needs to know you’ll be gone.

Check and copy (notarized) your passport.

Put one copy in your luggage and leave the other with a trusted friend at home.
Set any needed reservations. Prep your gear (waterproofing, name tags, expiration dates, etc.)
Check for any hazards (mines, pathogens, plants and animals) where you'll be working and brief your work crew. If going overseas, check the State Department's travel web site for warnings.
Estimate expenses and then add an additional 20% to help buffer unanticipated events. Start breaking in any new gear -- especially new boots.
Get dental checkup (for extended or overseas trips). Get medical checkup (for extended or overseas trips).

Starting at least two weeks prior to departure
Leave the name & number of nearest ranger station, police station, hotel, campground, etc. with someone at home. Set compass declination.
Return/renew any library books, rented movies, etc. Clear GPS receiver and set your field area's proper map datum.
"Empty" the fridge. Pay all bills, rent, fees, tuition, etc.
Hold or forward your mail. Purchase any items needed upon return (if returning at the last minute).
Hold your newspaper subscription. Charge batteries (for cameras, etc.)
Plan meals & buy needed food. Consider changing your answering machine message.
Get a set of spare keys for the vehicle you'll be driving in the field. Consider giving a set of your personal car keys to a trusted friend.

The Night Before Leaving
Check the weather forecast. Prep some ice and chill plenty of water.
Water the plants and feed the pets. Pack your lunch.

As you're leaving
Turn off your alarm clock. (Otherwise your neighbors might hate you as well as know you're not home!) Adjust the thermostat and water faucets if necessary.
Appliances off  (especially automatic coffee maker). Set timers for non-halogen lights and a radio in your home.
Close all windows. Do any last dishes and take out the trash.
Lock the doors as you go! If leading the trip, KNOW the NUMBER of people on your crew and write it down!!!