I am giving this practical solution by following the advice given by NIKKI ZERO COOL above, thanks.
To make it easier for you, when you kill saved enemies before looting bodies, this will allow you to find all the items you want, if you don't have the items you want to reload your game. Tip to be done on each body.
Focus on the hardware store to craft ammo and try to collect the rare items that are worth the most serum.
Ex: electrical components (30 serum)
Chemical components (20 serum)
Bone / alloy (15 serum)
If you have the level 1 (Renegade) "Sniper" skill, you can craft ammo (5) with 10 sera.
This greatly facilitates the extreme difficulties of the game, without forgetting to play most often in stealth, and to follow the tips given by NIKKI ZERO COOL.