There are 6 optional collectibles in Episode 3: Wastelands. Each optional collectible will unlock a specific achievement / trophy. If you have completed the episode, you can go back to specific chapters in collectible mode and not affect your decisions in the episode. Here are the timestamps for the collectibles:
0:36 - #1 The Dharma Bums 1:24 - #2 Train of Thought
1:49 - #3 Zero Hugs Given
2:29 - #4 Green Thumbs
3:10 - #5 Dancing Days
4:11 - #6 One of Us & Lost Boys Chronicles
Here is a video guide with English commentary!
Here is a playlist of guides for the game! https://www.youtube.com/playlist?list=PL-HeW6XkKdUJNaduS4UQz...