Type "/items" without the quotes.
Will give you a list of all the groundspawns in the zone, will not show what the exacty item is, it will merely show what graphics the groundspawn has.
Now, when you've decided which of these "graphics" you wish to pick up (search for my sgank.mac and you'll see examples besides the ones Armysoldier have given), you just "/itemtarget" that name.
F.ex. as Army wrote, in Kaladim you type:
/itemtarget *Red Mushroom0
/gank
Now you've picked up one of the Kaladim Constitutional shrooms.
/itemtarget *Blue Mushroom0
/gank
Now you've picked up the other of the Kaladim Constitutional shrooms.
Going to Elddar Forrest you could "/itemtarget 2H Staff" and you'd target bowstaffs that are on the ground. Follow it by a "/gank" and you'll have it on your cursor.