Anti-material Rifle (Five of Hearts) - At Unsan Village, there are anti-material rifle men near the number card. Once you incapacitate the Five of Hearts, you won't have them available anymore so make a decision if you want to keep the rifle or not. Unless you are really good with your sniper scope, the normal sniper rifle is a much better choice since you have double the ammo, and you may kill chopper pilots using either rifle (both rifles need to shoot through the canopy to be effective).
Vehicle Ammo Crates (Spades) - Various spots in the Chemical Complex and NK Garrison have vehicle ammo crates, presumably to refill your tank when your merc goes on a killing spree to pad ExOps' bottom line. If your NK Gunship-transport needs ammo, this would be a good time to take up the free ammo while in disguise. It saves you $6000 in operating costs.
Prototype Rifle (Spades) - Near the Chongju Farms area, several ROK female special forces soldiers will be milling around taking pot-shots at passing DPRK forces. Take one down (try luring one into your car with a promise to take her someplace exotic -- like Toledo -- then subduing her on a stretch of lonely road to avoid faction status damage) and nab a $16,000 weapon. The Prototype Rifle may behave like the Light Machinegun, but it can also fire while zoomed in. Don't let go of the sniper rifle though -- the prototype rifle's shots cannot pierce the canopy glass on choppers and does less damage.
Anti-air missile (Four of Spades) - This number card will have an Air-to-Air missile launcher to use against mercs who fly in without disguise or in the wrong chopper. If you want to keep this weapon, now would be a good time to pick one up for free.