get this, a small UAV helicopter
now I know what you're thinking, "they didn't have UAVs back then!"
well they didn't have explosive RC cars, sentry guns, and portable sam turrets either
here's how it works, you take it out, and briefely fumble around with some switches and buttons or something, then the motor comes to life and then it leaves your hands and flys around independantly
it is built using the same ad hoc appearence of the RC car and sentry gun. It has an onboard machine gun that it will use to gun down the zombies, which is it's primary purpose.
so basically, it is a portable, flying, sentry gun