If you happen to stay in a nice hotel or guest facility - leave those little lotions and shampoos behind, unused.
You'll save the overall cost of the room, in the long run - if enough people do it. Plus, you'll lessen the impact on landfills and the efforts of cleaning staff in replenishing those supplies.
Smaller containers use more materials in packaging than larger containers. Thus, when you use those, you're using more PVC per ounce. You get the picture.