Donating Elfroots is the most efficient way to get XP because you can buy them so cheaply from the elvish camp.

  See the Dragon Age Wiki Page on this topic for more info: http://dragonage.wikia.com/wiki/Allied_Supply_Crates

Donating Elfroots is the most efficient way to get XP because you can buy them so cheaply from the elvish camp. See the Dragon Age Wikia Page on Allied Supply Crates for more info.