Luggage works is the most prevalent, and all the bags are designed to clip on to the suitcase (or the J-hook, if it's a flight kit). The comments about commuting are pertinent. A lot of dead-heading will lead to the same issue.
As for "gear," like I said earlier, if your company has EFB's, that changes everything. If you need to carry Jepps, you tend to find a way to fill your flight kit. You need a decent suitcase, the bag for your flight gear (headset, sunglasses, flashlight), and the food bag.
Everyone has their own little bag of "I gotta have this" stuff. Some of it's obvious, some of it gets on your list based on some experience.
You'll learn to pack for the length of the trip plus one day (or for 7 days if you're on reserve). You need underwear, white t-shirts (once worn, a white T can double as your gym/running shirt at the hotel), one pair of gym shorts, one pair of shorts (summer) or jeans (winter), 2-3 pair of white socks, uniform socks and 1-2 T-shirts. If you commute, carry a collared shirt so you can ditch the uniform shirt when the trip is done. As for extra uniform stuff, I stopped carrying pants years ago, but I always keep at least one shirt in my bag. One pair of sneakers, a minimal shaving kit, and a spare phone charger that never comes out of your suitcase at home will round out your collection. In the side pockets, I keep a small umbrella and a warm pair of gloves.
If your company allows leather jackets, get one. It'll be expensive, but it will last you the rest of your life, and will spare you the blazer or trench coat in the winter.