Thankfully we're out of "L" and into Mark and Q land... where the chapters are shorter... and of course added centuries later (the chapter divisions, that is).
3:7 Brood of vipers...
This is "Q" material in the sense that it is common to Matthew and Luke and not in Mark. Interesting that Matthew adds that the people Jesus is speaking to are Pharisees and Sadducees. Luke says nothing of the sort. So, assuming a common source or that one of the two used the other, who added Pharisees or who took away?
Matthew is extra down on the Pharisees so it makes sense to say that he added it. But would Luke have deleted it? I can't say that I have an opinion at this time, although I suppose if we go with the standard idea that Luke is usually the more accurate picture of Q, then we would conclude Matthew adds that they were Pharisees.
3:8 Don't say, "We have Abraham as a father."
Reminds me of some of Paul's debates about who the seed of Abraham is...
3:10-14 What should we do?
This whole section is unique to Luke and fits with his general emphasis on social justice. No one can listen to Luke-Acts and not conclude that social justice is a major Christian concern.
Luke's gospel is the only one to mention that Jesus was praying when the Spirit descended on him, yet another characteristic theme of Luke-Acts.
3:22 "You are my beloved Son..."
Luke follows Mark's wording here, rather than Matthew's, where God speaks to everyone, "This is my beloved..."
3:38 "... of God"
I can't remember Luke's theology of the phrase "Son of God." This is something to track. The way he puts it in the genealogy, we are all sons of God, which of course we are, but Luke implies Jesus as son of God in the genealogy in this generic way.