So, you read the documentation, looked at the available samples and cannot find what you need.
If you are at all handy with a spreadsheet program (like Excel) - help is on the way.
Now you have a map to try with GPS_LOG. I would strongly suggest that you use the PC version ( GPS_LOG Win32.exe) to develop your maps.
Terrain features are more difficult. You can use Flight Display program to generate a text file that you then add to your map file.
Converting ESRI shapefiles to map files. You can still get free map data on the internet. Use companion ESRItoMAP program to translate them.
Converting ArcInfo (E00) files to map files. You can get free map data on the internet. Use companion DEMtoMAP program to translate them.
Converting Digital Elevation Map (bin) files to map files. You can get free map data on the internet. Use companion DEMtoMAP program to translate them.
For special use airspace take a look at the AIRSPACE and EUROSPACE programs by Carl Ekdahl, or WELT2000 by Michael Lorenz Meier, or if you can use Java classes at the samples provided by Yuliy Gerchikov.
Carl Ekdahl and Michael Lorenz Meier graciously included generation of GPS_LOG format maps in their programs.
If you import AIRSPACE generated information to your maps, make certain to scale radii accordingly. You can easily add fills by changing -4 symbols to -6, making certain that arc directions are correct ('@' and '#') and that you start and end each polygon with a -2 symbol line.
If you generate a huge SUA map (eg. whole United States) with Airspace and display it with GPS_LOG you will see that arcs and lines do not necessarily meet after you zoom in, and there is movement of arcs w.r.t. lines as you move map around. This is NOT an AIRSPACE issue. This is because GPS_LOG is optimised for drawing speed and assumes map areas of reasonable size for a glider pilot. These effects can be minimised to a large extent, by having the INITIAL map be displayed with a diagonal of less than 200 miles.
IMPORTANT: Currently Airspace program generates maps suitable for display, but as it is not using -6 symbol for arcs and does not always draw them in proper direction, nor does it use symbol -7, other restricted airspace functionality of GPS_LOG WinCE will not work. If you like that functionality with Air(Euro)Space generated maps please download the FIX-IT program (courtesy of Bart Janssen). It translates Air(Euro)Space generated maps into more friendly versions. FIX_IT program requires Visual Basic run time module available form Microsoft. If you cannot run it, download vbrun60sp5.exe.