Second or third the FRS or GMRS (license required, but a lot more power and a lot more sold than licensed) suggestion, they are good for short distances. The MX5 club in NH uses that (don't know if there's more than one) and we have a set we used to follow them in a Mustang GT (love the Coyote engine). If you are willing to do a very easy test you can get your amateur radio license and switch to 2m radios. BaoFeng do Yaesu knock-offs for about the same price as FRS radios but they work for much longer range. We use 2m for off road trips and have no trouble talking well out of line of sight, much better quality than FRS or CB, external antennas work better but a simple 2m antenna is less than 2 feet long. Noise cancelling VOX headsets make it like you are right there, so long as you don't both talk at the same time. We usually use mobiles, rather than HTs, a lot more power, sometimes hit repeaters from more than 200 miles in Nevada. I learned enough to ace the test in a couple of days, it's just multiple choice, though I did go on to extra class when I wanted to work HF.
http://www.arrl.org/getting-your-technician-license
The interstates mostly have solid cellular coverage, but we are on Verizon and have even had coverage in rural Nevada well away from main roads and towns.