I also recommend buying one of these hard hat inserts for your baseball cap, they are very concealable and will protect you against punches, falls, and even small rocks thrown at you. Other important thing that goes without saying, don't buy a knife online. Get one in a physical store and pay in cash while wearing a cap. If you really want to use something you bought online, wait a year before using it and don't buy easily traceable shit like a 500€ knife no one buys.