When I talk to students about their preparation for graduate school in archaeology, I've noticed that most worry one set of skills that are largely irrelevant for actual success in either a Masters or PhD program: those associated with a "field school." Yes, participating in the long-standing tradition of an unpaid apprenticeship in the field is still considered a "rite of passage" for archaeologists. However, what one learns in such an experience provides only marginal return when it comes to actual success in graduate school or even as a professional. All one can really expect to gain from a field school is knowledge that:
(1) You like (or do not) other archaeologists. Many field settings are remote and force individuals to cooperate and share daily living in a way that leads to somewhat intense experiences. Of course, such an experience could be accomplished doing just about anything (camping, ice slogging, sailing a dingy across the Pacific with 12 of your closest friends, etc.). What makes archaeological field school unique is that it forces you to hang out with other archaeologists. Since those who choose this sort of focus for their lives are an odd breed, it doesn't hurt to find out if you can stand 7x24 discussions with others who share the same bent view of the world as you do.
(2) An appreciation for the fact that archaeological field work is tedious, mind-numbing and occasionally just boring. It just is. Yes, one will have a lot of fun futzing around in the dirt but most of the "fun" comes camaraderie or reflections after the fact (usually over cold beverages in the light of the moon). But the work itself - well, for the most part, trained monkeys can do it. If you can see through the drudgery and still like archaeology, you might have a chance becoming an archaeologist.
(3) Some archaic knowledge about rote and tradition and little else. Most field schools tend to focus on simply repetitive activities that have long stood for archaeology -- "digging." Digging holes in the ground to retrieve artifacts is a time-honored tradition. However, the view that "digging" is a central skill in doing archaeological research is massively overblown and erroneous. Digging is destructive - archaeologists are the greatest threat to the archaeological record. The origins of such destructive field strategies comes from 1930s interests in stratigraphy for culture history construction as well as putting maximum numbers of individuals to work per the WPA and other Depression-era work programs. The 1x1 meter square, in fact, is a descendant of the 5x5 foot square that was chosen to be large enough to stick a person and a shovel in. The size of the unit has little to do with sampling: it is too big for small artifacts and too small for large artifacts (such as aggregate scale). The array of technology that permits one to study the record w/o excavation (and subsequent destruction) increases daily. Don't drink the excavation Kool-Aid... Even in Mycenean archaeology the practice is pointless, destructive and provides little in the way of knowledge about the record that cant be obtained in other ways. (This means you, Keep-the-table-empty Dude).
One caveat to this point: in CRM in the US there is a strong bias towards digging 1x1 meter holes as a means of bilking developers and lining the pockets of CRM company owners. Digging holes is expensive because of the labor involved and the subsequent activities required to deal with the stuff uncovered. This doesn't mean that much is learned by doing this -- even the best reports of 1x1 meter "test" pits simply state that "some stuff was found" since the samples uncovered have no known relation to each other -- but it does mean that someone is getting rich. Current estimates place the cost of a single 1x1 meter unit at more than $10,000. That's good coin. So my caveat has to do with the fact as a student archaeologist you probably should get your piece of the pie in order to make a living until you can be in charge and change this rip-off. So by all means, learn to dig a 1x1m -- just do it in the cheapest and most expedient way you can that gives you the street-cred to take a CRM position at your local archaeology firm.
Next up: What you do need to know before you start archaeological graduate school.