Peterwolf's TAB pick

Press Tab to grab the block under your crosshair.                              

 If that block is already in hotbar slots 1–9, Tab switches to that slot. If it 

 isn’t, a single ghost item is placed in an extra § slot between the hotbar and 

 your offhand. The next Tab replaces that ghost item and never dumps it into    

 your inventory.                                                                

 In Survival, Tab only selects a block you already have. The § slot is  Creative-only.                                                                 

 Default keys: Tab to pick, § (the key left of 1) to select the extra slot.     

 Both can be rebound in Controls.