Another interesting/ crazy idea from the Fine Living Network channel.
Instead of packing large bottles of shampoo & conditioner, pour the contents into a ziploc bag. When you get to your destination, either snip the corner of the bag and squeeze out like an icing tube, or simply scoop out what you need. At the end of the trip, you can discard the bags. If I used this tip, I'd probably pack quart sized bags with shampoo & conditioner inside a gallon size ziploc bag for added leak protection.