Without more information about the racing in your area as well as your own physiology you’re going to get a wide variety of answers to this question. I’d suggest you follow the same routine you’d do before doing a set of hard intervals. If you feel warmed up normally after 2-5 minutes of easy spinning then don’t do a warm-up. If you need to do a few hard efforts to feel ready to go then do that.
Everyone is different when it comes to warm-ups. For a 46 mile race I would do a relatively short warm-up with a handful of 30 second intervals, but no more. Probably I’d do them in my street clothes as I rode over to reg and back - so not a really serious thing 
Again - hard to answer without knowing your race conditions.
Personally I never race with any flat repair supplies and very very rarely see anyone with that in a race. I also don’t carry my phone, money, or credit cards like I would on a non-race.
At lower levels you will see more people with a saddle bag as there isn’t always a wheel van behind the field, but even when I was racing as a cat-5 I didn’t carry this stuff. I take the view that if I flat my race is over and there’s always a way to get back to the start (particularly on a short 12 mile loop) where you’re not that far away.
I’d suggest you bring the bag to the race and scope out the other guys in your field - if you see a bunch of bikes without saddle bags then you should be fine without one. If everyone has one then throw it on your bike