Special Old English characters on the Mac

Make sure you are using the US Extended keyboard layout:

æ	ALT+'
Æ	ALT+SHIFT+'
þ	ALT+t
Þ	ALT+SHIFT+t
ð	ALT+d
Ð	ALT+SHIFT+d
ā	ALT+a a
ē	ALT+a e
...	ALT+a ...
ċ	ALT+w c
ġ	ALT+w g
Ċ	ALT+w C
Ġ	ALT+w G