I would give them a separate gifts, because $100 is still a lot, and you can make more people happy.
I would definitely give some (probably 2 bills) to two different homeless people. This can buy them food or anything else they need, and could brighten their day. I would donate 100 to a charity I feel is important, to contribute to a cause and show my support. I would give one to my parents, whether they need it or just to show them I care, because they spent countless dollars on raising me. I would give my last bill to a food kitchen or some sort, so they could buy ingredients and things to feed a whole block of homeless people.