First, it is ok to get permission from the prison.
Lawyers are allowed to bring things in if they communicate with prison staff in advance. After all, for prisoners, it is necessary to supplement some material conditions in their lives, such as some important clothes, which can protect prisoners from the cold in winter. Moreover, by bringing some nutritious food to prisoners, they can be provided with adequate nutrition. After all, the living conditions in prisons are relatively poor and need to be improved appropriately.
Second, it is not allowed without the permission of the prison.
For some prisons, the guards may be strict, so there is no way to be flexible in contacting prisoners. Generally speaking, we can try our best to get some opportunities to send materials to prisoners by actively communicating and coordinating with prison staff. However, if the prison still adheres to the principle, it is impossible to carry out the work of delivering materials, and we can only simply meet the prisoners with the help of lawyers.
Third, it is ok for prisoners to greet prison staff in advance.
The prisoner greets the prison staff in advance, and the lawyer can deliver the materials. After all, for lawyers, in many cases, if prisoners communicate and coordinate with prison staff in advance, it will not cause some problems in the delivery of materials. Lawyers can also bring some clothes and food to prisoners for free, which can materially improve prisoners' lives and is a good way to visit prisons.
Note: For prison staff, it is often necessary to work according to prison regulations. If the prison regulations are strict, it is not feasible to transport materials.