stones and crystals generally perpetuate energies that increase the probability of prosperity rather than cause it alone.
I recommend some uncommon stones. Ones that offer protection in risky situations (bright orange carnelian on red silk), self-discipline and discernment (black obsidian and pakistani onyx), and just pure luck in rough situations (like deadlines, yikes! try a happy colored tourmaline, or a tourmalinated (sp?) quartz).
I recommend the carnelian be worn about the wrist or neck in some form of jewelry.
STORE YOUR OBSIDIAN AND ONYX IN SOMETHING EARTHBOUND, COOL, AND DARK.
Then I recommend making some sort of friendly, touchable trinket of the quartz or rainbow tourmaline.
The reason I think these are good is because they all draw on different aspects of personality levels ...positive energy, negative energy, ebb and natural flows of life..., and your friend will adjust to the one she/he feels closest to, and will use that one most often. I believe that crystals and stones should be stored where they can safely charge out of direct interaction with other items. So, try to cleanse and bless them before placing them in a safe material for presentation.
I am not a pro or anything... I just sort of knack at keeping my crystals healthy and happy like they are friends!