Now that I am older and wiser and less likely to want to schlep around a lot of crap, my gear has been streamlined into components that can be quickly tossed into the bag of the day and easily carried about. Now, whether I am going out for the day or leaving for a months-long vacation, I simply go to my gear closet and pack in less than five minutes.
Pick a bag. The first choice I need to make each day is what kind of bag to use. If I am just going out to the store my pockets will work or maybe a fanny pack (yes I know they are out of style but these are exceedingly useful). For a run, hike, or entire day out I may need a daypack. For a trip that includes car, bus, or airline travel, I will take a 30L backpack. For an overnight or longer backpacking trip, a slightly larger backpack will be used.
Next I pack up the items I never leave home without: cell phone (Galaxy Note 4), wallet, keys, sunglasses, pen, and tiny emergency packet (pocket knife, single packet of Tylenol, tissue, Wet Wipe, quarters, $100 in $20 bills, small flashlight, bandaids, ear buds, alcohol wipe, matches, floss, safety pin, back-up thumb drive, needle).
Depending on the situation I may or may not carry a concealed pistol (pistol--either a Keltec .380 or a Sig Sauer 9mm, holster, spare magazine).
Do I need tech? If so I take my Tablet (Galaxy Tab S2 8") or my laptop (Dell XPS 13"); occasionally both for longer-term travel. I also pick up the bag which carries chargers, a mini travel mouse, extra batteries for the mouse, a power pack and on-ear headphones.
Clothing. This varies by activity (gym clothes? outdoor clothes for backpacking? a slightly more extensive wardrobe for vacation travel?), and since everything is arranged in a single closet it takes moments to pick out the needed clothing. Additional items that may or may not be needed: hat, gloves, poncho, rain gear, puffy jacket, buff, etc.
Water and food. I generally never leave home without a bottle of water and a couple of granola bars. For day hikes I will take a lunch, for general travel I will pack an assortment of food and an extra (empty) water bottle which can be filled up once I pass airport security, and for overnight/weekend/week-long backpacking trips I will gather all necessary food plus toss in an additional water carrier and a water purification system.
Toiletries. For both urban and wilderness travel I carry a basic toiletries kit which includes: toothbrush, toothpaste, floss, mirror, comb, soap, deodorant, razor, tweezers, nail clippers, nail file, and Vaseline.
Fix it kit. This kit contains useful items to fix things that are broken and includes a basic sewing kit, folding scissors, zipties, rubberbands, and duct tape.
Medical kit. For overnight and longer term travel, I bring a more comprehensive medical kit which includes bandaids, alcohol wipes, antibiotic ointment, moleskin, benadryl, acidophilous, aspirin, Tylenol, opiod pain killer tabs, Super Glue, gauze pads, medical tape, condom, Ace bandage, Thera Flu, and Quick Clot.
Other medical items. Although I don't need these items, other people may so here is a list of other things people may want to pack: extra prescription meds, feminine hygiene products, make up, an Epi Pen, glucose tabs, glasses, and hearing aids/batteries.
Wilderness emergency packet. If I will be hiking (whether day hiking in the desert or multi-day trips) I toss in a packet that includes: sunscreen, matches, lighter, paracord, emergency blanket, compass, whistle, magnifying glass, electrolyte tabs, water purification tabs, bandanna).
Other backpacking gear. For overnight or an extended outdoor trip I pack a sleeping bag, sleeping pad, tent, tent footprint, stove and fuel, toilet paper, bear spray, bug spray, trowel, GPS, maps, headlamp/batteries, water filter system, mess kit/spork, Bonners soap, trekking poles, ziploc bags, pack rain cover.
General travel items. These include: air/bus/train tickets, passport/visas, an unlocked cellphone, extra memory cards, notebook, and power adapter.
Specialty packets. You may want to make up a bag for the shooting range, for your portable office supplies, items necessary for your work, etc.
Note that for a BOB, all of the kits will be dumped into my largest pack and sorted out later.
By making up a variety of component kits, instead of a variety of bags, you will always have the items you need without the massive duplication of items. I highly recommend LeSportsac bags for each packet as they wear like iron (even though they look a bit odd with weird colors and designs) and last for years.