Sounds like fun but I agree with what Kilimanjaro said. No booze! Atleast till after the guns are put away and you are off the range.
Safety brief of some sort and maybe designate a few safety officers. Take turns switching out so everyone can be in on the fun.
I might suggest having some timed events. Set up a course of fire and see who has the fastest time.
Incorporate different targets such as baloons, clay pigeons, soda cans filled with water. Place them at different distances. Shoot a relay with pistols then run another relay with rifles and time each person. The options are endless.
The number one priority is SAFETY! Then have fun! If you're on public land be sure to clean everything up.
Good luck stay safe and have fun!