Using this method you will be able to open the Golden Chest infinitely without losing any keys.
1. Hard Drive
2. USB or Memory Card
3. At least 1 Golden Key
4. Any Save
1. Physically disconnect your 360 from the Internet / Live
2. Move your Gamer Profile to a USB or Memory Card
3. Make sure your save is on the Hard Drive and your profile on a USB or Memory Card
4. Sign in, Start a game, warp to Sanctuary, save and quit. This is so that you start next to the chest.
1. With the 360 disconnected from the net/live, sign into your profile.
2. Launch Borderlands 2
3. Create game lobby and select your character
4. Launch game
5. Once you spawn into Sanctuary, REMOVE the USB or Memory Card that contains your profile. A message will pop up asking that your replace the card. DON'T! IMPORTANT!
6. With your profile removed, open the chest and take the contents. Your key will be temporarily lost. DON'T PANIC! Once you complete the steps the key will be returned to you.
7. Save and Quit. The items have now been saved to your character.
8. When the game returns to the lobby, hit the guide button and exit to the dashboard. IMPORTANT!
9. You will now be signed out. Reinsert the USB or Memory Card and sign in.
10. Repeat steps 2-9 infinitely.
Why does this work? Golden Keys are tied to your profile GPD, not your save. Inventory, however, is tied to your save. Since your profile is removed, the key isn't recorded as being lost. Result? Infinite purple items.
I tested this myself with 2 characters; LV19 Commando and LV29 Siren and it works perfectly.
DO NOT DEVIATE FROM THE ABOVE INSTRUCTIONS OR YOU MAY LOSE A KEY. If you follow the instructions to the letter it's guaranteed too work.
Enjoy all Purple, and Pink, gear!