I have the Auslig NatMaps 250,000:1 mosaic loaded on my GPS and use that most of the time. I also have the Hema series which I use when they are in range.
Then, for specific events (Camp Coffs, for example) I download the best maps I can find (for camp Coffs I stitched together a mosaic of screen prints downloaded from the Terrain function of Google Maps) and calibrated it using identifiable points for which I could get the coordinates from other maps (e.g. road junctions).
This one from some maps of Mt Mee that Cmohr printed out
If you have sufficient calibration points then OziExplorer "Load and Calibrate Map" function can produce a map from any bitmap picture. On the first and last picture the coloured lines are the actual tracks from OziExplorerCE overlaid on the maps - you can see that the calibration was slightly better for Mt Mee than it was for Coffs.