How to add multiple users inside a container which is built by using repo2docker and How to give sudo access to the user account which is used while running repo2docker tool?

I’m trying to build docker image by using repo2docker tool.

repo2docker --user-name antony --user-id 1000

     It's working fine with this command and I'm able to get docker image. 

docker -dit --name container name image id

To build docker container .

docker exec -it container id /bin/bash.

     By using this i can access docker container with bash prompt.I'm trying to create new users in side the container but i'm getting error " only ROOT user can create users" .
  1. Can we create root account docker container while using with repo2docker? if yes please provide me the necessary steps ,if no can you please provide how to get sudo access to the users inside the container which is built by using repo2docker?
    2.How to install packages or libraries inside a container without sudo access?

Thanks in advance! Quick response should be more grateful.