Whether a helper is paid or a volunteer Employers Liability is a good idea. Depending on your type of organisation, it could also be a legal requirement. Even if you are not paying workers, you still have a responsibility towards them.
Event insurance isn’t legally required, but it is a good option to consider. If you’re working at an event, the organisers or venue might ask you for proof that you have at least public liability insurance.
It depends on whether their insurance extends to people or businesses that use the venue. They might require you to purchase your own public liability insurance, so make sure you check with them.