Once upon a time, I spent six days in London and Hamburg with only one backpack. I haughtily refused (read: could not afford) to pay the airline's checked bag rates so I toughened up and threw six days worth of supplies into a bookbag and set off. If I may say so myself, I looked rather fabulous for the entire jaunt, so I have no qualms over sharing with you my tips on packing a bag for the duration of just three days and avoiding checked bag fees.
1: Lay out your fantastic clothing. I don't care how you dress, it is all grand. I am huge on traveling a lot with only a little but still looking like a classical vixen..I mean...lady. I also loathe being burdened by heavy, cumbersome luggage when I travel. I am 5'4" on a good day, so you're dreaming if you think I want to arrive in a new location with a hardcase bag that rolls and goes up to my hip. I am all about mobility!
So, grab a pair of jeans (jeans, unless you're rolling around in the dirt, are good for three wears), wear it on the train/plane/whatever on the way there, done a dress/short/cute top (girl clothes can roll up RIDICULOUSLY small) on Saturday, and drag those jeans out for your last day and return trip. Tights, leggings, and underwear can also all be compacted down into almost nothing! Grab a cardigan (trains and planes can get chilly, so can foreign cities!). Find 1 pair of shoes that will match everything and viola! Classy all weekend long.
Ladies: don't forget your lady stuff. You know what I mean! Danger, surprises, and unexpected circumstances may strike at anytime. Be prepared! Men: you too. Be safe. It is your responsibility too.
2: Gank all of your tiny shampoos/conditioners, awful Bic razors, makeup removers, etc and stick them in a container (top). I have two of everything. One set stays at home and the second is almost always either in my purse or in that container, ready to grab and shove in a backpack for travel. I keep all of my shower-y needs in one zip container, and my makeup in another (middle container). My makeup is almost always very natural looking with minimal liner, so when I travel I only take mascara, chapstick, rosey lip color, and cover-up. I'm too busy exploring to be worried about messing up thick, black, eyeliner! However, you might not be able to live without your liquid liner, and that's fine! Whatever works for you, most makeup products are small enough to fit in a tiny container. Keep in mind that your skin might not be used to the climate you're entering, treat it nicely with moisturizer.
PRO-TIP: Any liquid (shampoo, remover, etc) that you're taking with you NEEDS to be in either a plastic ziploc or something that is pictured above. If something busts open due to a change in pressure or other wear and tear, the last thing you want is for your valuable, lovely clothes to be covered in sticky shower stuff. Ugh. Been there. Never, ever again.
Lastly, have a purse (or your wallet, guys) stowed in the bottom of the pack to take out when you arrive at your destination. Chances are you don't want to lug around your bookbag with your clothes in it. I have a leather crossbody that I snagged from the Goodwill for $2. Note: always carry a picture ID and your debit|credit card with you. Always have at least $40-$50 in cash; you never know: you may need a cab or where you eat lunch might not take card!
I also keep a tiny book in the front pocket of my crossbody for writing down places I've seen, where I want to go, directions, etc, so I can remember everything and look 110% less of a tourist. Sometimes I'll even print out and paste in a tiny little subway map. I'm sly, I know.
3: I always keep a folder with my eticket, directions my to hostel/couchsurfing host and a receipt for both. I also have a copy of my picture ID in there just in case I lose the actual ID or the backpack is lost/stolen. I carry around a baglillion business cards as well, because I am a shameless self-promoter. If I'm making pictures of someone|something and a bypasser or cop asks, I will hand them a business card and explain what I'm doing. If I have some left over, I'll leave them on tables, on bulletin boards. You never know who is going to see your work. The more, the better!
4: Most importantly-take care of yourself. You never know when you'll be hungover..I mean, have a sinus headache, need cough drops, or take on a minor cut somewhere. It helps to keep these things handy in the front pocket of your pack. I also reccommend gum and snacks for the train/plane (if allowed). Make sure you pack any medications you're currently on and set an alarm to take them. I know how easy it is to be caught up in adventure and forget!
All of this should (and will) easily slip into your pack (I bought mine yesterday from the Goodwill as well, $2!!!!!). As you can see, there's still a little bit of room at the top for a book or a heat tool (such as a straightener or curling iron) for all your hair-styling needs!
If you are a person who doesn't wear makeup or style their hair, more power to you! Tons of room and less hassle. It is all about figuring out your absolute essentials and then paring down from there.
The leather bag is my camera bag, which if you don't make pictures/have 100 camera accessories like I do, is unnecessary. I'm taking a train to Boston this weekend and I'm more than excited to be on the rails again and to travel alone. It's a zen thing. :]