It's Not The Size Of A Suitcase That Counts; It's What's In It That Matters!
It's one of Murphy's Laws of Travel; if you check luggage, especially if you are changing planes mid-trip, the chances of recovering said articles in the same condition they were at send-off and at the anticipated time and place of arrival are slim. That law is doubled if there's something you desperately need in the luggage.
I quote Captain Lonestar from Spaceballs, "Take only what you need to survive!".
Three Good Reasons:
1. No matter what you are trying to prepare for, you won't use everything in that suitcase, and you will have lugged it all over for no purpose; your body will thank you for leaving half of it at home. 2. Everything you think you need will be available where you are going (unless it's a truly remote place, in which case you still won't need all the accouterments because there will be no place to use/wear/plug-them-in/etc.) All those extras are waiting for you at your destination for about the same price you'd pay at home. 3. Most hotels/B&B's offer shampoo/conditioner/toothpaste/toothbrushes/razors/etc for the traveler who needs them. Most of them have blow-dryers, if not already in the room, available at the desk, and they'll even deliver one to your room. This is especially handy if you are staying in a foreign country and didn't bring electrical converters for the ac/dc outlets. You can find converters for around $20-$50 anywhere from Radio Shack to Best Buy. Targus is a good brand to trust. Bonus: Don't over-pack clothes. They are heavy to cart around. You won't be changing outfits nearly as often as you think, because you'll be out and about exploring most of the time. There may be clothes that you find at your destination that you want to buy and bring home, and you'll need the space in your luggage. There are laundry facilities at your hotel/B&B/destination. You may think, 'but what if I need...' - you won't need it.
When packing, it is best to consider the landscape of your destination. If you are going anywhere but a modern city center, don't pack heels; walking on cobblestone/dirt in heels is a nightmare. Check the weather. Check your itinerary. Dress for comfort first, style second. Hats & scarves are a lifesaver. If you can find comfortable walking shoes that are stylish; kudos!
Take a watch/timepiece* if you are changing time zones; phones don't always work when and where you'd like them to. When you arrive at your destination, remember to reset your timepiece to the local time.
Take a day bag that is comfortable to carry and has different compartments and never put anything in it that you can't afford to lose; these are the best for your daily treks while you're traveling. Take a water bottle; always. Buy sunscreen when you get there, unless it's going to rain on your parade the entire time. Where there is sun, there is need of sunscreen.
It has become an evolutionary and continuing challenge of mine to pack all I'll need in one or two carry on bags and to never check any luggage. It's faster in and out of the airport/train station and there's no chance I will be without or lose what I need. Extended trips beg to differ, but this is usually the best way to go. Backpack and a passport, and out the door.