This is a repost from another thread, but I've been meaning to post my method here in this thread for a while now.
Anyway, I have the benefit of working in the CEMS industry and have access to some awesome 3/8" PFA tubing. It's way better than plastic racking canes or standard 3/8" beer hose because it's incredibly stiff and can hold a shape, but is still bendable and creates an asstight seal in a cobra tap. I cut mine into about 12-16" sections and cut an angle at one end. I jam the straight cut end into my cobra tap and slip a #2 bung over the tube and then the angle notched side goes down into any 12 or 22oz bottle and I fill 'er up, taking care to "burp" off excess CO2 with the bung. My bottles last FOREVER and it also works great with growlers if you have the right size bung.
When I first started kegging, I built a Blichmann Beergun clone out of spare SS swagelok fittings lying around our shop. It's a serious looking beergun and has two thumb valves going to a T which feeds across a needle valve (CO2 bleedoff) and down into a 1' section of SS tubing. I used it a couple times and it produces the same results as my buddy's beergun, but the PFA tubing method works just as well and I can bottle up a six-pack in under 3 minutes on my way out the door to a friend's house. Needless to say, the $150 or so of swagelok fittings are now just a fancy shiny paperweight in my brewbox.
We just cleaned up our shop (Company President is coming for a visit) and now I have a whole mess of 3/8" PFA scrap pieces that are just begging to be made into ghetto beerguns. People can PM me if they want some. Just provide your own #2 bung and cobra tap hooked up to a keg and you're all set.