I admit, most of the time I use the shampoo and the conditioner in the hotel, and in most cases they have good quality haircare products. In fact, some of the beauty products I have found at hotels are now my favorites. However, I do budget travel as well, and the quality of the hotel reflects directly on the quality of the haircare products in the room, and I usually take my own with me, just in case. Also, if you travel (and especially fly) all the time, your skin and hair will need extra care.
I seem to have hard time sometimes finding products in the travel size, but scored big at T.J. Maxx a while ago, and found the Giovanni Cosmetics FLIGHT ATTENDANT First Class Hair and Body Kit, with Tea Tree Triple Treat shampoo and conditioner and cucumber body wash and lotion. The set is $7.99 and comes in a clear ziplog bag, ready for your flight.
And of course, you can always just fill in the small bottles you get from hotels again and again to avoid buying travel sized products. Also, Pitotubes sells fancy travel sized bottles in clear plastic bags for carry on flights. I find the price a bit too much, $42 for the set of 6 bottles in a bag, but they also sell the bottles individually.