1. Well-watered plants can be placed inside a plastic bag. Prop up the bag by using wooden dowels or something similar to keep the plastic off the leaves. Make sure the enclosed plants will not receive full sun as heat buildup may cook them. Bright, indirect light is best. Plants should keep for about a week with this method.
2. This method requires an old dish drying rack, a bathtub in a bathroom with some natural light and some shoelaces. Place the drying rack upside down in the tub and add several inches of water. Push one end of a shoelace through a drainage hole on the bottom of a pot and into the potting soil of your houseplant. The other end of the shoelace dangles into the water. What you have made is a wick system that will replace water in the pot as the plant uses it. Plants can last a couple of weeks if you have enough natural light.
3. There are numerous commercial products that can be used to automatically water houseplants in your absence. The advantage of these products is that the houseplant does not normally need to be moved. All require a reservoir from which water is either siphoned or pumped to individual houseplants. Houseplants should last as long as the water holds out. (Ward Upham)