They should carry over provided you didn't die while you were using it. I know this because Jeff usually has a good amount of them stocked up by the end of the game. But yes that was a wise choice. RC Cars are nice but like Spy Planes are better for general use. Spy Planes help enhance not only you but the whole team. RC Cars can only provide you with 1 kill. More if you're really lucky. However RC Cars are very good when a lot of people are using Ghost and/or camping. Though RC Cars are also a very good choice to use on Nuketown. It was probably an Attack Helicopter. Blackbirds require
7 with Hardline). Both are good choices too.
