College Fest: Junkyard wars/Treasure Hunt suggestions

My college is holding a techfest

I want to ask you people about 2 events

Please give your valuable suggestions for the same

1) Treasure(Tech) Hunt

Please help with the types of clues that can be given and the types of treasure that can be placed

2) Junkyard Wars

What type of materials or junk are mostly needed or can be used. Also the things that can be made using them

Thanks