action editor

how to combine two separate actions into one?

with the nla editor

I mean like, when two animations are on separate bones/objects

to have the data in one action -

Since camera and plane are two separate objects, you can only have an action per object, not for both together.

You could set up an armature with two unconnected bones, one for the plane, one for the cam.
link cam and plane to their bones, then animate the bones. Because the bones are part of one armature, you can merge actions by copying keyframes from one action to the other in edit mode (select action, Tab --> turns green and shows keys in the DopeSheet/ActionEditor).

and how about baking? two actions in one

just you could have about twenty objects with different actions - creating one metarig for all objects probably it will be awesome.

and in big animation objects / skeleton in different scenes are used in different ways.