Total noob
To answer your question above, I have a tote that doubles as a passable cooler. I bring fruit, yogurt, granola, pre packaged Trader Joe’s salads, and leftovers and eat them on the road. Not everyone does this, I would say about half bring some sort of food setup. I found that it helps me keep weight off and saves money. If I fly international legs at the start of a trip or an all Mexico kind of trip, that doesn’t happen since customs will take it all. I keep it cold with a wal mart pharmacy ice bag and ice from hotel ice makers. I usually bring enough to supplement 2 to 3 meals and snacks along the way. That way I still enjoy food on overnights but may eat meals while I fly or sitting in the lounge before or after a commute. I also bring either oatmeal or breakfast bars for breakfast since I am a PM flyer and usually don’t want to emerge from my room prior to noon.
I bring a yeti style cold cup because I don’t like drinking water out of the cans and I prefer it cold during the summer especially. My tote has a pocket for it on the side which makes it easy.
Again, this is just what works for me and it has evolved over 3.5 years on the line.
As far as a commute uniform, the only thing required for the jumpseat is no shorts, sneakers, or t shirts. Jeans are fine. Same for the training center except you can wear your Jordans there.
Best of luck in training and enjoy yourself.