Jason, 2003 thru-hiker, used a Garmin Vista. He was able to delete the maps that came with it, freeing up enough space to put ALL the maps for the CDT in it. He carried it in a little case attached to his backpacking strap. He says if you don’t bring a GPS with all the maps in it that you will be lost for days at a time.
I called Garmin and they said you couldn’t delete the basemap it comes with so I bought a Garmin 60c with 56 megs of memory just to be sure I would have enough memory. I was able to store all of the maps for the trail plus a pretty big corridor around the trail and still had lots of room to spare. I used the Garmin MapSource CD ROM (USA TOPO). Jason sent me his list of what maps he used off of Garmin’s Mapsourse Topo USA CD. list of maps to download into your GPS
2003 thru-hiker, James sent me his list of waypoints. If you download all the waypoints to your GPS it becomes pretty clear what maps you will need. Here is a link to his waypoints http://skylab.org/~crow/blog/gps/jamescdt03.wpt. He deleted some to make room for the final stretch so here is his final list. http://skylab.org/~crow/blog/gps/cdtfinal.wpt. They are in Garmin PCX5 format. They actually were in Mallegen format when I got them, so they needed to be converted by using this GPSBabel program. http://gpsbabel.sourceforge.net/. Using this program you can convert waypoints into what ever format you need them to be in. James, has them already in Magellan format at his site http://cdt2003.info/how.htm