Creating a custom User Role (e.g. "User can reserve items but can't delete them from reservations")

You can create a custom user role that allows a user to add items to a reservation without letting them remove items from a reservation. 

1. Go to Administration > Site Administration > User Roles > Add Role
2. Name your new role (e.g. "Reservation add, not remove")
3. Select the specific permissions you want that role to have