Luke, Paul and Galatians
It is generally accepted that Luke did not have access to the letters of Paul. However, Heikki Leppä has concluded in his dissertation, "Luke's Critical Use of Galatians", that Luke did use Galatians. I have not read the dissertation but Antti Mustakallio has provided me some examples from the dissertation that support this conclusion. I am only going to discuss one example involving the use of the Greek word συμπαραλαβὼν in Gal 2:1. Paul tells us that he and Barnabas took Titus with them to
The fact that the Greek word συμπαραλαβὼν also appears in 3 Maccabees may undercut the force of this dependency on Galatians since Luke has also used Maccabbees as a source for words. However the significant point about this example, as noted by Leppä, is that Luke and Paul use this word only in connection with Paul and Barnabas taking a companion with them on a trip.
Finally, I should note that Antti Mustakallio has indicated that Richard Pervo has cited this dissertation in his new book, Dating Acts.