I made this idea project last night, but here are some more details. I found an article the other day, and apparently you can use a simple Arduino as a virtual keyboard and have it enter whatever keystrokes you want really, really fast. Usually, you bring it on-site and plug it into the target device, and it executes an attack or something. You can also disguise it and leave it on the street for some unsuspecting person to pick up and plug into their computer or laptop, the only problem is the official rubber ducky from Hak5 costs about $80 and is on backorder, dunno about you, but I can't just leave $80 lying around on the street to possibly get broken, heck I can't even afford to spend that and not lose it. my solution is to get some of these ($6 for 10, so that's about $0.60 each)

and hook them up to a little (yeah, it's tiny) microcontroller ($10 for one or $25 for three, which is $8.33), 

put some code in it, and see what happens! This project will take a while as I've been super busy with life, so hopefully, I can get a working prototype sometime early in the new year; so follow if you want to see the completion.