Bike Locks

A bike lock is a very cheap way to ruin someone's day. The obvious trick would be to lock someone else's bike. Take it a step further and lock two random bikes together.

Then if you're feeling really evil, you could lock down any business that has those double doors with handles. Additionally you could also chain a car wheel.

The more you're willing to invest, the bigger the following chaos will be. Even super heavy duty bike locks are fairly cheap and can be bought for around a hundred. But in this case you don't need a brand new lock so you could search for used ones at garage sales or on Ebay.