If I could choose just a few things for you do in an afternoon near Newberg, they would be as follows:
Evergreen Aviation & Space Museum: This is a great place and if you have wanted to see the Spruce Goose, it’s here! You could certainly spend a lot longer than an afternoon here, but it can be toured and enjoyed in just a few hours if that’s all you have.
Downtown McMinnville: A great place for everything you are looking for! The rooftop restaurant at the McMenamins Hotel Oregon would be a great place for lunch and then let the shopping begin! Downtown McMinnville is filled with shops and sites and delicious places to find good food! You could certainly spend hours just enjoying it!
You can also enjoy visiting Sleigh Bells between McMinnville and Newberg: I love this place! It is a huge gift shop and I am sure it is filled to the brim with Halloween and Fall items right now. Sleigh Bells is also a working Christmas Tree farm so take the tour if you go! Last time I was there, they were serving tea and I know they had some homemade goodies such as fudge for sale. There’s a lot to see there!