The Amusement Park Physics, order code AMPK book describes several methods for collecting data from roller coaster rides. If you are starting new, the best products to use are:
Wireless Dynamics Sensor System, order code WDSS
Data Vest, order code DV, $54
Note that the best practice is to set up a "download station" at the park, where someone stays with a laptop. Student groups go out to collect data, then return to the download station to move the data from the WDSS to the computer, save a file with the student names, and do some analysis.
#1 Tip for collecting data from roller coasters: Test out all of your equipment BEFORE you leave for the park. Do some dry runs at a local playground so that you and at least a few of your students are comfortable with setting up data collection, then retrieving the data when the experiment is over.
A great web site with tips and tricks for data collection on roller coasters is: