I was so glad to have a couple of friends, some cap guns and rubber knives. We learned a huge amount of stuff through experience on a boring Saturday morning.
The hardest part is training yourself to ignore what is coming for the sake of realism. Other lessons:
1) Carrying concealed is a huge advantage over an enemy who is brandishing a gun, all told, amounting to several seconds advantage.
2) A karambit knife is so popular for zero distance self defense that they are making rubber versions of it for training.
3) The pistol-knife trench combo is the way to go indoors.
4) Hiding a knife behind your forearm is good for uncertain situations where brandishing a gun could be problematic. At the first hint of a problem, the knife is out and hidden, so you can be more relaxed about your gun draw.
5) A knife is good for “another player has entered the game”, behind you, scenarios. Cheap shots suck.