Even for being an elite Agent, things cost money. Pick up everything, whether you need it or not. Do not worry about filling your bag up too quickly; you will have plenty of room to start with. You can sell what you do not need later. Be on the lookout for fabric, tools and weapon parts also; these have no limits and you can pick up as much as desired. Do not be afraid to go up a scaffold, in a window, or down an alley. Most of the good items is on the streets, and not in the stores.