About the reserved seating, if you don’t have the time to watch the session on How to re:Invent here are my takes:

Reserve first seats for chalk talks and smaller session because they are usually filling up faster than others.
Leadership sessions have reserved seating but the Keynotes don’t, you have to be there sooner to get your spot. There are ways to see the Keynotes from outside of the room in places specially prepared for this.

Some tips I have received over LinkedIn and also found in this nice article:

Wear comfy shoes
Pack a bit of water and some snacks
Have a backpack (keep it lightweight if possible)

Let me know if this was useful to you and please share other tips and tricks if you have some 🌟 .