Usually depends on the game. every mario game i simply call them "shrooms" then call the mega mushrooms "red shrooms". sometimes i'll be playing one of the mario games, and suddenly blurt out "Yay shrooms!" when i get one. but in other games, i simply got me a life. very seldom i'll use the term "extra life"
Hmm I never thought about shortening Mushrooms to just "Shroom". I did call Fire flowers just "flower" though since, there was only one kind for the longest time. Now there are at least 3 types of flower power-ups.
Depends on the game, mostly. I often say "extra life" or "life insurance". If it's Spyro I might say Dragonheads; if it's Crash I might say Crashheads; if it's Medievil I refer to it as Bottles or Jars; and if it's Jersey Devil I just call them FFFFUUUUUUU's.