First of all go to your minecraft folder in finder so in finder go to your username/library/Application Support/Minecraft when in your minecraft folder go into your bin you will have a thing called minecraft.jar when you find it right click it and click open with archive utility if you are like me i cant open it because mine wont work with that if so you must compress the minecraft.jar so bring it onto your desktop and right click and press compress minecraft.jar you should get a zip and then you should be able to open it with archive utility and a folder should come up name it minecraft.jar
if you dont know how you can right click the folder get info and change the name when changed it should work and heres a example go to the link make sure to delete the 2 mojang items in the meta inf folder dont delete the folder just the two mojang items in it you should have 3 items and also delete the minecraft.jar items but not the folder
www.minecraftforum.net/topic/140684-173-toomanyitems-in-game-invedit-july-1/
Download it and open your minecraft.jar folder and open the toomanyitems folder copy and paste all the items from the toomanyitems folder into the minecraft.jar and there you should have the toomanyitems mod when done have fun!