From my perspective, it's usually easier to raise coin (or
barter items) and buy your DI preps in bulk rather than
relying on the free ones you can get on the ground.  The
pick-up-for-free ones are handy, though, if you're already
ranking in the same area (or very nearby).  In that case it
doesn't "cost" you any additional time/effort to
just pick it up each time you make a pass through the area.