I take three very different ones. Scale down toiletries. Take small or nearly empty containers whenever possible. Check out the travel sizes where you buy shampoo. Baby shampoo can quadruple for shaving, washing out clothes, and for bath soap.
Most hair conditioner works well as a moisturizer for hands and body.
Plan to buy things once you are there. Shampoo, wool sweaters, saline solution, travel journals, even a guitar have all been procured by Cornellians once they have arrived. No customs agent is going to let you in with drugs that don't clearly belong to you. Oh, yes, and a handkerchief. Many experienced travelers feel that a tiny flashlight is an essential.