Well most consumer electronics are meant to accept 120V AC current and then use an internal or external (power brick) to convert it to some specific DC voltage(s). So, your friend is correct, you'll need a converter, also called a power inverter that will take 12V DC in from the battery and convert it to 110-120V AC to use normal household electronics with. Thing is, you don't have to plug in into a cigarette lighter. You could easily mount it out of the way somewhere like under a seat and wire it directly up the battery. Then plug your game system into it and you're set.
Be careful tho. Many inverters have specific power limitations. So before you get one, you should find out exactly what the current draw is of whatever device you plan on plugging into it.
