I found out something interesting
When using wxAuiToolbar, if you add the code below, the toolbar items are much more packed. If you don't call it, the default is similar to calling it with a paddeing value = 3. My toolbars are created with wxSmith and I tried to find such an option in the properties, with no luck. So I added the code below outside the auto-generated code:
As mentioned, I think Code::Blocks is not using wxAuiToolbar, but wxToolbar? I could not find the SetToolBorderPadding(int padding) for wxToolbar, but there is something similar
In the documentation it says "The default value is 5.". Maybe this is a clue, although it does nothing for the vertical size.
EDIT: there is also
PS. ok I see what you are saying about images, will consider