Okay, here's the deal: If you're ordering takeout from a counter service place, tipping is appreciated but not necessarily expected. Those employees usually earn a standard hourly wage, and tips are just a nice bonus.
BUT. If you're ordering your takeout from a dine-in restaurant, you really should tip about 10%. Your server still had to take down your order, check everything to make sure it came out correctly, and package it up nicely for you. That's precious time taken away from their tables — and they aren't being paid much of anything for it. So tip.