Walkie-Talkie info

If you like driving with friends, you will find that having radios makes these trips much more fun, and safer.

Radios really only work line of sight. Any FRS/GMRS radio will work. The Motorola ones seem to work best. They are simple to use and get the job done.
If you want something with slighy better range you can get a FM/UHF/VHF radio like a Baofeng UV-5R+.

They are more complicated to use and require programming to get the most out of them, which can be a bit of a hassle. See below for stuff that will help with that. Get this programming cable.

CHIRP: Use this desktop application to program your radio.  In that program open a file or make your own, connect the programming cable to your radio and computer, and upload the file to your radio.
Frequencies Free by Jaap Crezee: Phone app that can be used to convert a FRS channel into MHz, to enter into a Baofeng radio. The are other free apps that do the same thing. Note that entering sub channels (x.1, x.2) requires a bit more radio programming.