Use superglue on your co-workers' and bosses keyboards, flip them over and press them against their desks. Put superglue on the bottom of the keyboards and the sides so all attempts to remove them will be extremely tedious.
Zip lock bags can be used as incriminating evidence when containing a select few plants. Place them around your workplace and call the police for a drugs bust.
Advise your boss that you won't be coming in for your shift as you found a way to travel through time and you're going to go right ahead and travel to get next month's wages.
Concentrate all of your energy on finding out your boss's most deep and dark secret. When you find this out, post large card signs everywhere that exhibit this secret for all to see.