Build a Solar Still
If you come across a dry riverbed or are in mountainous terrain and can get to the Southern base of a mountain, you can build a solar still to gather at least a little water.
Find a spot that's damp in the morning and is going to get direct sunlight later on in the day. Dig a hole that's 4 feet wide and a few feet deep. Lay your tarp across the hole and place rocks or sand on the edge of the tarp to hold it in place. Place a single rock or a couple handfuls of sand in the middle of the tarp so the middle is the lowest hanging point over the hole.
Put a cup directly under the lowest part of the tarp. Now comes the hard part. You have to sit around and wait for the sun to do its job. It will evaporate the water in the soil, causing it to rise up into the tarp. As the water hits the tarp it will pool up and run down the tarp to the lowest point, which is where you've placed the cup.
This is a very slow process, but may be your only way to get water in an arid environment.