Link node 1 to node 2 and create list
This can be done using a combination of Editable Views and Entity Reference. 

You will need to create an entity reference field on one of the content types that points to the other. Then create a view of that content type.

Using editable views you can have a select list to add an entity reference on the company node to the event node. If you set up the entity reference field to allow multiple values, you will be able to have one company attending multiple events.

You can also create a view that shows all entities that reference the the event in order to show a list of all companies who will be attending an event.