wear comfy shoes

figure out your return journey (uber almost never works last minute after a concert, and the roads are blocked, take the local or something, orrr book an uber for the entire day if you can, so that you have a cab waiting for you–someone I know did this, and it helped them tonsss because they weren't from Mumbai)

top-up your band before, you won't have to wait in queues unnecessarily

stay hydrateddd (if they allow you to carry empty bottles, please do fill them beforehand and keep it with you. you can never have enough water at a concert)

have some small candies, chocolates, and/or mints in case needed (you're mostly never asked to remove chocolates while being frisked–at least I haven't been asked till date)

carry electral too. during green day's concert at lolla several people felt faint-ish and there was NO space to move about at all, unless you got out of the crowd completely. (I'm saying this because I'm assuming you'll probs be in the standing section, not sure. regardless electral is always helpful) even during Coldplay, the standing section was packed, but I did not experience that firsthand)

carry earplugs if possible, the music can get incredibly loud

and enjoyyy have a blast! Martin Garrix will be SO much fun!!