Which word - spoonful, scoop, head, slice, bar, stick?

I want two ............. of bread. slice  /  slices  /  stick   /  sticks

I only want one .............. of ice-cream.   head  /  heads  /  scoop  /  scoops

May I have a .............. of pizza?   spoonful  /  spoonfuls  /  slice  /  slices

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