Lots of scenario games that get played on a weekend can be pretty equivalent to a scenario paintball game. When we say "Milsim", we mean "weather-enhanced boredom".
The kit you listed covers all the beats you need to hit if you can access your car a few times throughout an event, but none of the ones you need if you'll be sleeping uncovered on the ground for a total of 6-8 hours over 48. That's why you got dogpiled.
Don't forget to pack extra extra batteries, and another extra for the guy who didn't bring enough!