An empty water bottle can be used as lots of different tools and vessels with the right nohow. You can use them to store cordage, make a spoon and bowl, Funnel, scoop or even a fish trap to catch some food.
Water bottles can be recycled into numerous items in a survival situation or for regular everyday uses. Survival tip for taking everyday items to improvise for survival uses.
Find more info on Bushcraft and survival here.