Quote Originally Posted by Kawaii Ryűkishi
Shaking particular guards, with profound amounts of luck, will yield rations. I was speaking in terms of even Normal and Hard mode, though.
Snake would also hand you ration(s) during the Tengu mini-boss corridor.

Although I wish Kojima did leave in the FAMAS, and while it may not fit into the context of the Tanker chapter, he could've at least made it a dogtag reward, or something you can find after a number of playthroughs.