Valid passport for nation of permanent residence (U.S., for example).
Proof of personal helath insurance (see International Student Identity Card for an option on this), or a letter waiving COD's responsibility (contact Dr. Staeck for information).
Special visas are NOT required unless you plan to stay in the Czech Republic longer than 90 days.
Personal funds for gifts, additional purchases, or personal travel.
Photo identification in addition to your passport (in the event such is required).
Textbooks, assigned field manual, and writing implements.
At least a month's supply of any prescription medication that you take.
An up-to-date tetanus shot.

This is nothing more than a guide to things that you need, or might wish to have, for the Czech field school.

Strongly Recommended
A valid International Student Identity Card and its supplemental insurance (cost ca. $20)
    Link to check this out   or call 1-800-2-COUNCIL  
All appropriate vaccinations for adult Americans.
Camera and film (it is cheaper to bring it than to buy it).
Over-the-counter medicines, such as ibuprofen, aspirin, antacids, anti-diarrheals, etc...
Extra room in your suitcase or an extra bag for gifts.
An extra set of prescription glasses (if you wear them).
An American-Czech Dictionary or phrase book.
A small personal sewing kit (really, this may be very useful for those unexpected tears).

Recommended Field Gear
Durable clothing that can get very dirty, at least 2 sets.
Sturdy boots or shoes that support your feet in working conditions.  Water resistance is useful.
Leather-palmed gloves (not gardening gloves).
A good hat.
Durable rain gear you can get dirty.
A student-sized backpack for toting personal gear.
A sweatshirt or some such for field work on brisk mornings.

Items of Personal Interest You Might Consider
Shampoo, soaps, toothbrush, deodorant, etc...
A bath towel (these will not be provided in most cases).
A walkman with headphones, and a FEW of your preferred tapes/CD's.
Personal reading material.
Appropriate material for personal needs.
A couple sets of comfortable, casual clothes.
Good walking shoes, however you define these.
A pair or two of Gortex socks have been recommended by some of the more "outdoors" aficionados.