Do I need internet access to activate the five Headhunter and Ultimate Vault Hunter Upgrade Pack 2 for Borderlands 2?

The Headhunter Packs and the Ultimate Vault Hunter Upgrade Pack 2 were released after the Game of the Year Edition and no subsequent PC, Xbox 360, or PS3 retail versions were produced that would have included them on disc.

The Borderlands Handsome Collection, only available for Xbox One and PS4, includes both Borderlands 2 and Borderlands: The Pre-Sequel, as well as all DLC produced for each game prior to March 24, 2015. This is currently the only way to get those content packs at retail.

There is no easy way.

Since borderlands 2 uses steam DRM, you'll need internet access to activate the DLC even if you'd somehow get a code in meatspace. You could try moving your steam installation without the games (for storage usage reasons) on an USB stick or laptop, activate the DLCs on a computer you have internet access on and then copy the changed files back - this should make it possible to use the upgrade pack without ever connecting that specific computer to the net.
The Headhunter packs need new files though, so you'd have to install the game somewhere with internet to get them(sharing game files is against steam ToS I think)(hash checking tools might help you to cut down the size of the data you'll need to transfer).