My advice: make a packing list. Scrutinize it carefully. Ask yourself if every item is necessary, or whether you can substitute another item that will do double-duty (e.g., shorts that can be worn more than once, a sundress that is also a swimsuit cover-up, body lotion with sunscreen). Note on the list which items you will wear when traveling so you don't have to pack them (e.g., your bulkiest shoes, your jacket, etc.). Strive to make it the most efficient, awesome packing list in the history of list-making (which, like war-making, is a prestigious line of work, with a long and glorious tradition).
Once you've decided that the list is complete and doesn't contain anything that you're not very likely to need, then start packing. PACK ONLY THE ITEMS ON THE LIST. Be ruthless. You are a one-woman army and your marching orders are THE LIST. When your husband casually says, "I thought maybe I'd throw in this extra pair of socks," or "you don't mind if we pack separate shave gels for your legs and my face, do you?," stand your ground. Slap his insolent face with an empty, flaccid packing cube and yell, "NOT ON THE LIST, Buster! You want extra socks? Wash out your day 1 socks in the sink and wear them when they're dry! One shaving cream is the limit, you overindulgent sunnovabich! The list is SUPREME! OBEY THE LIST!" Once the bags are packed, put them in the car (or somewhere that you can't conveniently slip in additional items).
Perhaps I'm being a tad overdramatic, but this isn't not too far off from what I do (the packing part, I mean - not the domestic abuse part). I like to pack efficiently and fit everything into carry-ons, while my husband is a former Eagle Scout who likes to "be prepared" for all possible eventualities and always wants to throw in random items at the last minute. ("What if our plane heads North by mistake and we crash in the Arctic Circle? Let's pack a harpoon, some tin dishes, and a jerky-making kit, just in case... and this paddle-ball... and this lamp... that's all I need".) THE LIST has been our saving grace: once we've agreed on its contents, we don't deviate from it. We pack light, we're well-prepared, and everyone is happy.
I used to be an overpacker, too, but I can't tell you how emancipating it has been to become a "carryon-only" family. While others will be collecting their checked bags or fretting over when Magical Express will deliver them, we'll be coasting by with our carryons in hand and the wind in our hair (at least, that's how I'm imagining it, LOL!). For example, for our upcoming trip we are taking 3 carryon bags for our family of 4. Bag #1 has breakfast foods and snacks, and miscellaneous items like nightlights, bedtime storybooks, cell phone chargers, an empty laundry bag, toiletry kits and our 3-1-1 ziploc bags (in an outside pocket, for easy removal at security). Bag #2 has my clothes and my daughter's, and Bag #3 has my husband's and son's, all packed in packing cubes. For a 6-day trip, each person packs 5 shirts, 3-4 shorts (some shorts to be worn twice), swimwear, PJs, sandals, socks and underwear. We'll wear sneakers, pants, jackets and T-shirts on the plane. If we need to do laundry, we will, although we've never had to in the past, and there will be plenty of room in the carry-ons for souvenirs (much of it vacated by the snack/breakfast foods) on the return trip. I know it's a leap of faith to leave behind some of those things you "might" need, but I think you'll find it's worth it.
