gistfile1.rb

MUL = 100 # normalize to whole number

def random_item
        items = items.merge!('' => (100 - items.values.sum.to_f)).sort_by { |k,v| v }    
	percentile = 0 

	items.each do |loot,prob| 	  	  
  		percentile += prob
  		return loot if rand(100*MUL) < (percentile*MUL)
	end
end

I don't think you want to be re-calculating that random value every time.