Take the plant together with some soil around its roots and place it in a plastic cup or cut the lower part of a plastic bottle and use it as a cup. If neither is available, wrap a wet paper napkin around roots and soil, then place it in a plastic bag.
If the roots come out without any soil, place them in water, using any kind of container you have. If you don't have a container for water, follow the wet napkin method, but be careful to wrap it gently, otherwise the roots might be damaged. The plastic bag keeps moisture inside, prevents the napkin to come apart and protects roots from accidentally tearing them.
Keep the leaves outside the plastic bag if the weather is hot.