I use a packing list, which is fine-tuned for each trip. For me, the list takes all the stress out of packing: I know that if I've checked off every box, nothing has been left behind!
Our packing follows a general progression: we pack the day before, but it all starts a couple of weeks ahead of time.
About 2 weeks before we depart, I finalize the list. I refill prescriptions and do any necessary shopping for grocery items (we bring our own breakfasts), sunscreen, new toothbrushes, dollar store ponchos, new sunglasses or sandals for the kids, etc. Then I do all the laundry, select and gather outfits for each of us, and start to assemble them in spare laundry baskets (1 for each person). This keeps everything organized and visible (and unwrinkled), and allows for easy access if we decide to change or add anything.
The day before we leave, I carefully roll and zip all of our clothes into packing cubes, and pack one 21" rolling carryon per person. Food items then get bagged and packed into the extra space in the kids' carryons. (They're 5 and 6, so their clothes don't take up a lot of space yet!) All non-liquid toiletry items go in the extra space in my carryon (I recommend the eBags "Pack it Flat" toiletry case -- it's amazingly compact and easy to pack), and DH and I each put a 3-1-1 "liquids and gels" ziploc bag in an outside pocket of our carryon for when we go through security. Since we typically depart early in the morning, I also lay out our "travel clothes," generally comprised of the bulkiest items we plan to bring: a comfy pair of long pants, a T-shirt, a sweatshirt or fleece, and sneakers for each of us.
Also the day before we leave, we pack all of our "personal items" for the plane. For me, it's my crossbody purse (which serves as my park bag) with ID, credit card, camera, phone, sunglasses, a mini first-aid kit (a baggie with band-aids, alcohol wipes and blister pads), hand sanitizing wipes, all travel documents, etc. For DH, it's a backpack with reading materials, headphones (if flying JetBlue, which has the seat-back TVs), his sunglasses and hat, inhaler and epiPen (his asthma and allergies like to travel with him) etc. The kids each take a small backpack with their Crayola Color Wonder sets, a couple of new activity/sticker books (plus any homework from school), their own headphones, and a "care package" of apple wedges, Twizzlers, raisins, and similar snacks.
So far, so good -- we've never had any trouble carrying our own luggage, forgotten anything we needed, or brought anything we didn't need, and unpacking at the hotel takes no more than 10 minutes.
