I've competed in 3 hackathons and organized 1. Here's what separates teams that ship from teams that are still debugging at demo time.
Pick the Right Stack
Pick what you know, not what's impressive. I always reach for Next.js + MongoDB because I can scaffold a full-stack app in 30 minutes.
Define the MVP at Hour 1
Write down the single screen a judge needs to see. Build that first. Everything else is optional.
The 4-Hour Rule
If you haven't shipped something that works by hour 4, pivot. The sunk cost fallacy kills hackathon teams.
Demo Engineering
The demo matters more than the code. Practice the happy path. Make it look good. Hide the rough edges.
Sleep
Non-negotiable. 4 hours minimum. Exhausted code is buggy code.