To cheat the system and receive more life crystals and stuff out of a chest, do the following by using the multiplayer feature:
1. Go to Terraria.org and download their dedicated server program. (Simply scroll all the way down at home page)
2. Use it to start one of your worlds or make a new one. (To join your own server, type "localhost" into the IP address [without quotes]).
3. Search for a life crystal or chest that has something you want to keep getting and save the game through the server command window BEFORE you pick up the item.
4. Pick up the life crystal/chest item and close the server window. You should lose connection In-Game.
5. Re-open your server and join it. You should still have the life crystal/chest item in your inventory.
Rush back to the spot where you found the stuff to see that they will still be there. All you need to do is take the item and close the server without saving, and you can just pick up whatever you want over and over again.