If you want to make sure you don't forget anything important for your vacation, it's best to start the packing process days or even weeks before your departure date. This gives you plenty of time to draw up a complete list and purchase any additional items you may need. I personally like to start packing a week in advance, as it allows me to add items as I think of them and also reconsider my choices and remove items. We usually pack 3 to 4 weeks before a trip to make sure everything fits and we don't need anything that needs to be ordered.
Then, 2-3 days before we leave, we unpack and go through the checklist to make sure nothing has been missed (like the wrong contacts, a charger, or not enough medication). It's best to pack in stages; pack things you won't need at home 2 weeks or more in advance, then add outfits 3-4 days before the trip. Finally, pack your toiletries, chargers, and electronics the day before departure. When packing, make sure you focus on the order in which you'll need things.
Have a set of pajamas for everyone on top so you can easily grab them on your first night. Trying to carry very light luggage in order to travel with only hand luggage is often a mistake. I have a packing list that I always update (especially after a trip) and I buy most of my clothes with travel in mind. When it comes to things like bikinis and sunglasses, be decisive and choose one or two pairs.
I have this blank printable list that you can use, or this list of checklist styles that you can use to plan your packing. Resealable bags are great for packing because they can be used to organize makeup, seal dirty underwear, make sure liquids don't spill all over your clothes, and much more. Unless you have a good reason for wanting to travel with only carry-on baggage, plan to pack a real (large) suitcase. Anything related to your sleep routine (makeup remover, facial wash, etc.) or morning routine (makeup, contact lenses, etc.) should go in your carry-on baggage.
Pack your carry-on carefully, including the essentials you would need in case your airline loses your checked baggage. You'll have time to fine-tune your outfits, leave out unnecessary items, and help others pack for their travels. Many people wait until the last minute to pack their belongings in their suitcase, but others may have their things stored for months. I check my basic packing list about a month in advance to make sure I have the right items on hand. Overpacking leads to its own set of problems such as excess baggage charges, damaged baggage, and no suitcase space for souvenirs or purchases abroad.
There's no reason to be messy; before my next trip I'm going to become someone who delights in suitcases and guarantees a good time!For me, clothes are always the hardest thing to understand so I always start there and choose a color palette.