I was active on GMRS for many years, but I also had my amateur license. I used GMRS because I couldn't get others in the family to get their ham tickets.
We, and everyone else I knew, all ran CTCSS tones on the GMRS radios specifically so we/they didn't have to listen to any other traffic. The idea was that it was for family use, and not for making random contacts with people we didn't know.
-only exception was the 462/467.674 141.3Hz "traveler info/emergency" channel.-
Other than that, we used one of the simplex frequencies for family use, with the CTCSS to make it so we didn't have to listen to other users, and we had our own tone on a high level repeater that gave us a lot of range.
So, like others said, many GMRS users are not looking to make random contact like you'd get on CB or amateur radio. I'm sure there's some, but it is infrequent. I'd say do not spend good money on GMRS gear if that is your intended use. You will be disappointed.
But, if you really want to do it, get the right gear. Don't get the consumer grade stuff. Get a commercial UHF radio that has the -required- FCC Part 95 certifications. You can get a hand held, but for driving use you really want an antenna outside your car. Using a hand held inside the metal body/tinted windows is going to severely limit your range.
Something like a Kenwood or Icom commerical UHF radio. Personally if I was doing it, I'd do a Kenwood TK-8180 mobile and put a permanent mount UHF antenna on the roof of your car, and another one at your home.
There are a number of technical reasons you want the commercial gear, but I'll hold off going into that right now.
Bonus is, when you get your amateur license, you can program 70cm amateur radio frequencies into those radios.
But, really, if you want random contacts while on the road, get one (or both) of the following:
A decent CB radio with an efficient antenna mounted on your vehicle.
An amateur radio that will do the VHF 2 meter band.
The ham license is not hard to get, and gives you access to a lot more users that are interested in making random contacts. GMRS will be a disappointment on that front.