How much garbage do humans generate?

More than they need to. The figure changes depending on your actions. If you define food waste as garbage, then A.youre not composting it and B. youre wasting food. If you buy everything in a load of plastic bags then throw them away, youre generating excess waste. Im sorry, I want to give a figure like 12 trillion tons, but the figure is alterable depending on how much we care. Its a bit like asking you how much you swear, you can control it.