Each multiplayer map has some point where you can get supplies (stock up your ammo / grenades).
One always seems to be near the drop off location, but the other are spread around the map.
Where are those points exactly?
Here's a rough sketch of Reactor, the red circles are the ammo boxes.
Glacier(Missing 1?? This map might only have three.):
Condor(The upper right one may be a little off; need to double check it):
Need to play this map a few more times to get a sense of its shape.
Not pretty, I know, but hopefully gets the point across. I miss any locations, let me know in the comments and I'll add them in.