I don't know what restaurants YOU go to, but servers that I am familiar with don't just stand around. In this area, servers are run ragged. It is nothing for one server to have 4 to 8 tables to take care of at all times. High end establishments may have a better server to client ratio.
And if all they do is bag a meal to go, how much of a tip would that deserve that is not already expected for their wage?
I often tip 20%-25% for good table service for a meal where I'm there for 90 minutes. How much of a tip should someone get for the 10 minutes it takes to bag a to-go order?
-PJ