You have just purchased your plants and are overjoyed at the thought of planting them... Unfortunately you need to wait until next weekend due to the bad weather.
What should you do with your plants ?
Leave them in the back of your garage in total darkness ?
In your living room ?
Well, neither is the best solution.
Regardless of the species of plant
The most important thing is to keep the roots moist. Spray them regularly, but do not overdo it and do not let the water stagnate. Effectively a root that is deprived of air and hence oxygen will end up rotting away.
Storing young plants that are either balled or in a container
Regardless of how many days you might need to wait, and especially if it is likely to be hot, take care to keep the centre of the root ball, especially if it is small at a constant humidity. To do this unwrap the root ball from its packaging to water it more easily and then wrap it up again in newspaper. It is better to spray the root ball rather than soak it, as this avoids loosing the soil that surrounds the roots. Store the plants upright preferably outside but protected from frost.
Storing plants in containers
As the volume of soil is bigger than for young plants where there is just a root ball, it suffices to just water them from time to time so that the earth remains moist. Keep your plant outside, preferably protected from frost.
Storing bare rooted plants
The roots of these plants are not protected by soil and it is up to you to look after them. There is effectively a very high risk that the roots might dehydrate. Take care of your plants as soon as they arrive. Put them into a pot or directly into the soil, in a sheltered position (against a wall or hedge). Cover the roots of your plants with some sand or compost up to about 5cm above its collar and firm it down. Outside lean your plants against a wall or hedge that will give them some shelter. If in a pot keep them outside protected against the frost and rain. Water them lightly if they are dry, this will also keep the roots moist. You can keep plants in this way for several days before they are planted in to their final position.
Someone has given you a plant and you do not want to plant it for several months ?
Select a large enough pot and fill it with a mix of soil and compost so that you can provisionally plant your present and look after it (unless of course your plant is already in a container).
Water it regularly but not too much.