I used the bombwake wakeflag holders, at this point I have 2 which is a bit much at $65 a pop but they are really high quality and you gotta rep' your country...
For the flag pole I used a chimney sweep extension, they sell them at lowes. A small amount of electrical tape helps keep them in the holders tight but I wouldn't hesitate to use them without.
The extensions are nice and flexy, and if you use a pretty thin material flag (i.e. cheap) they are good up to 35 mph.
The fittings on the chimney sweep extensions are NPT so you have to get creative, but zipties and a small fitting does the trick.