The best way to ensure your plants thrive when you have to leave town is to ask someone else to care for them. Barring this, however, there are some things you can do to at least keep them watered while you are away.None are foolproof, and the effectiveness of such methods depends on how long you are gone and what the weather is like. Still, your plants will at least get a small amount of water, which can be the difference between life and death.
Move your container and hanging plants to a cool, shady location. The cooler your plants are, the less water they will lose to heat and evaporation.
Prune any flowers, including buds that are ready to bloom, off the plants, as maintaining these flowers (and fruit, if you choose to remove fruit) takes a lot of water.
Water your plants thoroughly. Soak them until they are dripping and overflowing. Cover in-ground plants with several layers of wet newspapers.
Insert a self-watering device into the soil as close to the plant's roots as possible. Push it right through the newspapers for in-ground plants. These devices are usually globes with a long, thin hollow spout. The spout is pressed into the soil, and the water slowly leaks out.
Make your own watering device with an empty plastic soda bottle, if you do not have self-watering globes. Fill the bottle with water and try to position it lower than the plant. Then, soak a cotton "wick" in water, and insert one end of the wick into the soda bottle. Place the other end a couple of inches into the soil of the plant. The fabric will draw up the water from the bottle to the plant.