Work to confirm a solid headcount. Having this will help you when making food and swag orders. Generally, events see a 30-50% attrition rate, so make sure you consider this in your planning. Make a plan for what to do if you have more sign ups than your event is being planned for. If you exceed your initial goals you might need to make a waitlist. Try to give priority to hackers who are closer to your event since they are more likely to actually show up.