Typing collect <item> will allow you to gather several of that type of item at once. Under the new exp system in DR, this appears to teach foraging at least as well as individual forages and is better for learning perception. I suggest using grass or rocks.

When you look at pile, you may notice that members of each guild have a different appearance to their foraged piles.

Barbarian: A crude heap of grass with bits and pieces of foreign matter sticking out at odd angles.
Bard: An artful arrangement of grass that might resemble a pile if you stare at it long enough.
Cleric: A cairn-like mound of grass.
Empath: A pile of grass skillfully arranged to prevent the materials from shifting, at least in public.
Moon Mage: An archaic configuration of grass that might look like a pile in a different light.
Paladin: A heroic organization of grass boldly holding itself together against all odds.
Ranger: A perfectly arranged pile of grass in which each piece rests against the other in a delicate balance that preserves its natural essence.
Thief: A misshapen pile of grass that looks vaguely like it could be someone else's pile of grass.
Trader: A neat collection of grass organized by weight and market value.
Warrior Mage: A loose stack of grass that looks almost like a bundle of firewood.

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Thanks to Drevid, Dyanara, Grisleaf, and Naeya for help with the above list.