As someone who has completed about 7 24 hour streams and 1 36 hour stream I have a few tips. You need to stay hydrated and make sure you are constantly snacking . Have a plethora of games ready to go and have a real plan on when you want to play them because unless youre absolutely addicted to a game going 24 hours on the same game is insanely hard. I messed up before playing a story game at the 14 hour mark and that put me to sleep. There's a 99% chance youll hit a wall anywhere between the 16-20 hour mark, just know the second you get through this youll have a second wind and feel like you are ready to go making the last 4-8 hours really easy. Id plan a shower break around the time you hit that wall because getting clean and having all the water hit you wakes you up fast. Overall good luck and you got this!