Re: Things to do in a mehndi - other than sing/dance/play music
dear bollywood diva! a’salam.
mabrook on your wedding 
please take time before your wedding, to sit down with your parents and discuss with them, that celebration, dancing, singing and music are permitted in islam at weddings and eid.
i dont want you to spend 5 hours not doing what you had wanted to do initially..which is just to have some fun with your friends before you’re married.
playing the drum…aka ‘dholak’ in urdu…*is *allowed. why not make use of that permissibility..and get the party on? you know that there are several ahadith, which clearly show that Prophet Mohammed pbuh clearly stated that singing, and dancing is allowed.
i come from a very orthodox muslim family myself..and yes i’ve become very rebellious in some aspects, but there is nothing wrong with your celebration of your mehndi. mehndi itself is NOT a part of an islamic wedding..but consider it a party being held in the event of your marriage. 
i hope you will talk to your parents about this, and if they remain hard headed…please do NOT hesitate to go to a masjid near you, and ask an alimah for a fatwa.
best of luck to ya hun!