While reading through Luke over the past couple weeks, it seemed to me that Luke makes explicit ideas that are implicit in the other Synoptic Gospels. I note here four: (1) the exodus motif, (2) the movement of the Synoptics' presentation of Jesus' ministry from Galilee down to Jerusalem, (3) the idea that Jesus was a prophet "in word and deed," and (4) the belief that Jesus rose physically and bodily.
Much has been written on the presence of "new exodus" typologies in the Gospels. Only Luke, however, speaks of Jesus' "exodus." All three of the Synoptics tell the story of Jesus' transfiguration (Mt 17:1-13; Mk 9:2-13; Lk 9:28-36). Each mentions that Moses and Elijah appear and talk with Jesus. But only Luke says "they spoke of his exodus" (ἔλεγον τὴν ἔξοδον αὐτοῦ). Granted, ἔξοδος doesn't necessarily mean "exodos," but as François Bovon states,
Ἔξοδος is thus a euphemism for death, but Luke knows that this is not God's last word. Jesus' journey leads from Good Friday to Easter, and finally to the ascension, which Luke will narrate like a separation and an ἔξοδος ("exodus," "departure"; see Luke 24:50-51, ἐξήγαγεν ... ἔξω, "he led them out"; and Acts 1:9-11). It is entirely possible that he also has in mind the fundamental experience of Israel, the exodus from Egypt.
The Movement of Jesus Ministry
In John, Jesus goes back and forth from Galilee to Jerusalem, but one thing that unites the Synoptics is the movement of the story from Galilee to Jerusalem. To see this in Matthew and Mark you have to zoom out and consider the big picture. Luke 23:5 states it clearly, as the religious leaders respond to Pilate,
But they insisted, saying 'He stirs up the people teaching throughout the whole of Judea, beginning from Galilee unto here!'
There is mention of Galilee at the end of the other Synoptics. For instance, in Matthew 27:55, after Jesus is crucified, Matthew states that many women had followed Jesus from Galilee to minister to him. At least to my mind, however, these statements do not highlight as clearly that Jesus' ministry has been presented moving linearly from Galilee down to Jerusalem.
Jesus, a Prophet in Word and Deed
This is implicit in Matthew 4:23-9:35. The Sermon on the Mount (chs. 5-7) proclaims the kingdom in word, while chapters 8-9 proclaim the kingdom in deed (chs. 8-9). These chapters are framed with summary statements, which say that Jesus was going around proclaiming the kingdom and working miracles.
If you think big picture, it is clear that this section of Matthew is portraying Jesus as a prophet “in word and deed.” Luke states it explicitly: On the road to Emmaus the two disciples tell of “the things concerning Jesus of Nazareth, who was a mighty prophet in deed and word (ἐν ἔργῳ καὶ λόγῳ) before god and all the people” (Lk 24:19).
A Physical, Bodily Resurrection
Dale Allison’s Studies in Matthew is my favorite biblical studies book, hands down. In the essay titled “Touching Jesus’ Feet (Matt. 28:9),” Allison makes a persuasive case that when Jesus appears to the women at the tomb and they rejoice and “clutch his feet” (ἐκράτησαν αὐτοῦ τούς πόδας), one of the points being communicated is that Jesus physically rose from the dead. Ghosts don’t have feet, and as Allison argues, that idea was widely understood.
Luke does not leave it to the reader to connect the dots. When he appears to his disciples after he has risen, he says,
Look at my hands and my feet, for I am he. Touch me and see, for a spirit does not have flesh and bones, as you see that I have.
Perhaps these things are stated explicitly in other places in the Synoptics, but these passages stood out to me and sounded particularly straightforward in comparison with Matthew and Mark.
 For example, David W. Pao, Acts and the Isaianic New Exodus (Baker Academic, 2002); Rikki E. Watts, Isaiah's New Exodus in Mark (Baker Academic, 2001); R. T. France, The Gospel of Matthew, NICNT (Eerdmans, 2007), pp. 80-81, 105, 127-128, 988.