The number one rule is to PACK LIGHT! We were gone for 10+ days and only brought carry-on suitcases and small backpacks. We wore everything twice, and I don't regret it. Definitely leave room for shopping! There are so many great finds in Europe. Our suitcases were stuffed coming home - as in my zipper busted open. Ha! I didn't list everything we packed, but these are the key items.
Comfy + Cute Tennis Shoes: these are essential! See photo of matching shoes. We wore ours hiking in the heat and with dresses to our fanciest dinner. Keep in mind: your shoes will get filthy! And you will walk dozens of miles.
Sandals: thick-soled sandals or flip fops are a must. I wore my Tory Burch flip flops and had trouble walking because the pavement is so uneven. You really need shoes with good support.
Mom Bag: KJ's bag saved us. She made me promise that I wouldn't take pictures of it, but I'm glad I broke my promise. See below. She searched for the perfect bag before we left town. The flap unzipped so she could keep our important documents and her credit cards extra safe. Not cute but practical! I had a mini purse but wished I had hers.
Dirty Clothes Bag: usually a Target sack. I pack this even when I'm just going to the lake. I hate when my dirty clothes touch my clean clothes.
Tote Bag: Lululemon bags are the best! I'll unload things like my toiletries, shoes and bathing suits into my tote so that I can sort through my suitcase easier. We also used my tote as our beach bag.
Headphones with Adapter: for the plane.
Snacks: I packed 6 granola bars, and we ate all of them. We also kept our leftover snacks from the plane to eat whenever we got hungry.
Hand Sanitizer: a must!
Mouthwash: for after your plane or train reaches its destination, and before you get to your hotel to dig for your toothbrush.
Copies of Passport: bring your passport and a copy with you. Keep them in different places so that if one goes missing, you have the other as backup.
Water Bottles: we mostly drank out of plastic bottles, but we did refill ours a couple of times.
Pens & Pencils: just because.
Outlet Converter: do research. KJ has a really good one. It was like a power strip!
Rain Jacket: so glad we had these!
Umbrella: I brought black and blue minis. In Florence, everyone left their umbrellas in a bin at the door. We found the blue one but could not find my black one. There was a similar one there though so I think someone took the wrong one. Either way, I now have a much nicer black umbrella. Ha! But lesson learned: carry a baggy with you so that you don't have to leave your umbrella in the bin and risk losing it.
Socks for Flying: I like to fly in sandals and bring tall socks in case it gets cold.
Sunglasses for Flight: this is for KJ! She slept with her sunglasses on.
Tide To Go: I so wished I had one. I spilled spaghetti on myself twice.
Face Wipes: also wished I had these! It would have been nice to freshen my face before dinner.
Portable Chargers: Life savers! We used these every day. Both of our phones died constantly.
Allergy Medicine: I usually don't have allergies, but I did on our trip. The buildings are very old so there's lots of mold, and you spend a lot of time outdoors.
Hair Dryer: don't bring! Every place we stayed had one.
Neck Pillow: don't bring! It's so bulky, and we were always on the move. If they weren't borrowed, I would have thrown it away. They also got really dirty.
Inside Out: something I regularly do when packing is fold my clothes inside out. This keeps lint and dirt off of your clothes so they're nice and clean when you put them on.

We bought a little something everywhere we went.
Barcelona: we got matching white tennis shoes to replace the rose gold and black ones that we literally wore the soles off of! I also got a white jean jacket. I wanted one for so long! 
Florence: so many things! I got a matching rose gold necklace and bracelet. I wear them both daily! I also got some statement earrings and a fun leather strap for my clear purse. We both got leather bracelets with a fleur de lis, the crest of the city of Florence (& go Kappa). KJ got the same charm on a necklace. We bought matching leather belts and some Christmas goodies for our fam! We also fell in love with post cards so we bought three each.
Sorrento: I wished I could have bought gallons and gallons of that tea I mentioned! Instead, I bought a golden yellow jacket to wear to work, and we got mom a purse for her birthday. We also bought more post cards here, which I hung in my bathroom at home. 
Madrid: slide-on shoes at the market! They're basically silver Birkenstocks with the cutest sole. 

150 Euros per Person: we only took 100 euros total, and that was huge mistake. See our taxi incident in Capri. A few places and some transportation (i.e. the taxis in Capri, trains and buses) only accept cash.
Call Your Bank: again, refer back to our taxi incident. KJ's card got declined. Thank goodness for dad!
Cell Phone Service: since KJ and I are on the same cell phone plan, we took turns using data. She would use her phone for 24 hours then I would use mine. You can get WiFi most places, but we found having cell service was really convenient. It was $10 per day. Our service didn't work great in Positano but most places, it was just like home.
Wear Sunscreen: we did! The sun is harsh.
Airbnb: this is the only way to go! Bookings.com canceled our room a couple of days before we left. I was really nervous about finding a different place, but we found an Airbnb for much less than our original place. Airbnb is so handy because everything you need is on the app, and you can share all of your stays with your travel buddy.
Google Maps: I say download before you go. I think they work better than regular Maps.
Potty Paper: we almost always found a free restroom, but some places, like the train station, charge 1 euro to use the restroom. We frequently found, even when you pay, the restrooms don't have toilet paper. We got a roll to carry around with us. Ha! But seriously, it came in handy.
Mani + Pedi: get a mani before the trip and a pedi after. You walk so, so much, and the ground is dirty.
Fly Direct: we flew to New York on Thursday and flew from there to Madrid on Friday afternoon. Flying from DFW to NYC to Boston to Madrid saved us $900. On the way back, we flew from Madrid to NYC to DFW. When it was all said and done, I would have rather paid the extra money to fly direct. NYC for a day was fun though! We walked 7 miles around Central Park. As we were sipping wine at the airport, our flight from NYC to Boston got canceled. Eeek. Luckily, American booked us on a direct flight from NYC to Madrid. We had to shuttle (happily) from LaGuardia to JFK. Instead of arriving in Madrid at 5 a.m., we arrived at 7 a.m., which worked out better anyway because our train to Barcelona didn't leave until 9:30. I love logistics, but this was too much!
Don't Trip: one thing I have failed to mention in all my posts is how many times I tripped on this trip. Ha! The sidewalks are so uneven. I tripped real good in Barcelona, like had to catch myself on KJ or I would have gone down. Note: no alcohol was involved. This left me temporarily disabled. I couldn't bend my knee at all so I hobbled around like I had a peg leg. The worst part was going down stairs, which are everywhere in Europe. A couple of months later and my knee is still sore, and I'm still avoiding running. Whatever you do, don't trip!
Find a Travel Buddy like KJ: but good luck! Easy-going, well-prepared, always-matching, photo-loving, laughs-at-everything, comfy-as-a-pillow travel buddies aren't easy to find! We had the time of our lives. This trip will always be the most special.