Hey mane. This is an exxxxxcellent question. When I'm traveling, I wanna look my best and travel light, so the first thing I ask myself is "where am I going, what am I gonna need, and what's the weather?"
WHAT I PACK
The goal is to get everything into one carry-on, with one zip-top canvas tote. I like my dopp kit to be small, packed with the usual suspects, plus Band-Aids, Neosporin and aspirin, just in case. I am usually on business – so I bring a suit typically – but you can skip that and get away with a jacket or two, navy or something discreet. (Even on vacation, it's good to be prepared.) I always pack a white shirt (in case something formalish comes up), always pack a solid tie, a pair of white jeans, a pair of blue jeans, and a pair of dress shoes that can be dressed up or down. If I've got room, a pair of more casual shoes like moccasins or loafers. Even if it's not fall or winter, I typically pack a lightweight sweater – a fine-gauge cashmere crewneck. Cashmere is sort of God's polar fleece... it packs so easily and is great for layering. And, no matter what, a swimsuit. It's the biggest disappointment when you don't have it. Be ready always... to go swimming.
HOW I PACK IT
I like to wear a jacket on the outbound flight – it doesn't wrinkle as much, gives you a leg-up on a possible upgrade, and all the pockets make it like a man's version of a purse. You can get a lot in there. If I'm bringing a second jacket, I first hang it on a plastic wide-bodied hanger – ask your local haberdasher for one of their castoffs. Then, I'll cover it with plastic like you get at the cleaners, and put it in a lightweight garment bag. I will section the garment bag into thirds, folding the bottom up one level, laying my ties across the middle section so they won't move around, then folding up again neatly. And that goes on the top of one side of my carry-on.
Shirts – there's a formula to this. I'll take one additional shirt for every 3 days I'm gone (4 for a 3-day trip, 8 for a 6-day trip, etc.) and I get them folded in plastic when I send them to the cleaners (Ralph's on Collier, by the way,) because they're easier to pack. You can use the plastic as your laundry bag, too. For jeans, I will turn both pairs inside out, and roll them up so they avoid getting stained (white) or staining other items (indigo). I'll usually bring a pair of shoe trees, but those things are heavy, so in a pinch, you can put some rolled-up socks and underwear in your shoes instead... it works almost as well. If I've just got the shoes I'm wearing, I'll put my socks and underwear in a felt shoe bag. And that's about it for the suitcase. One more tip: when you get to where you're going, hang everything up – and when you hop in the shower, move the stuff on hangers to the bathroom to enjoy the steam and ease up any wrinkles.
In my tote – you want one with a zipper so you can put it underneath your seat without anything falling out – I put my computer, a folder of work stuff, another felt shoebag filled with cords & adapters, my sunglasses, some reading materials that I probably won't get to, plus some pens and something to write on. You have to watch out for the kind of pens that explode on planes though. Ink stains don't come out easily.
I know I say this a lot, but ultimately dressing – whether you're on the road or on the tarmac or just on the clock – is about good manners. Be practical and comfortable on the flight, sure, but make an effort for those around you. You never know who you're going to run into at the airport... and in a funny way, it doesn't matter. To sum it up: look nice, pack light, bring a pair of swim trunks, and never underestimate the importance of those felt shoe bags. Travel safe and buon viaggio.