You must level up and purchase all the upgrades for Batman. You will be provided all but 3 gadgets. One is available for pickup up after you finish up at the Museum. Another one is not available until the second time that you visit the Steel Mill. The last one requires that you complete the first four AR Training exercises. You will be notified of the side mission when a new gadget is available. The code to hack TYGER security terminals is considered a gadget as well, you will get this at the end of the game.
You must complete the "Bargaining Chip" achievement to unlock the gadget from the Steel Mill.