Since the OP is a U.S. citizen I sort of assumed they planned on entering Thailand on a 30 day tourist visa expemption, so no need for a visa just a stamp at entry and then one at exit. Note that the Departure portion of your Immigration documentation (TM-6) will be stapled into your passport, removed by Immigration upon exit, stapled to your boarding pass and then collected by the airline at the gate. For those who might require a visa, those take up an entire page, at least they do in my case; one-year, multiple-entry Non-Immigrant B visa.