Can I play with remote-control toys?

Go for it. Just keep the antenna at least 6 inches away from your device, and pointed away from your body. If it's closer than that, pacemaker reversion, inhibition, and ICD shock are possible.   Also, a word of additional advice: starting a remote-control helicopter courier service seems like good idea at first blush, but there's no way to turn a profit with all those crashes. Trust us.