Search online for "counter flow bottle filler" I have one and although it takes some practice they work. If I had to do it over I would check out the Blichmann beer gun.
For portable beer from the keg made easy I just use a growler or save plain seltzer plastic bottles, stuff a piece of vinyl tubing in the tap and fill them. It won't stay carbonate for long but enough for short term and a lot easier.
Another option is to fill a few bottles when filling your keg and prime them with Domino Dots AKA sugar cubes. One per 12oz bottle or do the math for larger.